MPLX MPLX LP

Exhibit 1.1

EXECUTION VERSION

MPLX LP

as Issuer,

and

MPLX GP LLC

as General Partner,

$1,650,000,000 5.500% SENIOR NOTES DUE 2034

UNDERWRITING AGREEMENT

May 15, 2024

May 15, 2024

To the Representatives named in Schedule I hereto

for the Underwriters named in Schedule II hereto

Ladies and Gentlemen:

MPLX LP, a Delaware limited partnership (the “Partnership”), proposes to issue and sell to the several underwriters named in Schedule II hereto (the “Underwriters”), for whom you are acting as representatives (the “Representatives”), the aggregate principal amount of its debt securities identified in Schedule I hereto (the “Securities”), to be issued under the senior indenture, dated as of February 12, 2015, as supplemented by the First Supplemental Indenture, dated as of February 12, 2015, the Second Supplemental Indenture, dated as of December 22, 2015, the Third Supplemental Indenture, dated as of December 22, 2015, the Fourth Supplemental Indenture, dated as of December 22, 2015, the Fifth Supplemental Indenture, dated as of December 22, 2015, the Sixth Supplemental Indenture, dated as of February 10, 2017, the Seventh Supplemental Indenture, dated as of February 10, 2017, the Eighth Supplemental Indenture, dated as of February 8, 2018, the Ninth Supplemental Indenture, dated as of February 8, 2018, the Tenth Supplemental Indenture, dated as of February 8, 2018, the Eleventh Supplemental Indenture, dated as of February 8, 2018, the Twelfth Supplemental Indenture, dated as of February 8, 2018, the Thirteenth Supplemental Indenture, dated as of November 15, 2018, the Fourteenth Supplemental Indenture, dated as of November 15, 2018, the Fifteenth Supplemental Indenture, dated as of September 9, 2019, the Sixteenth Supplemental Indenture, dated as of September 9, 2019, the Seventeenth Supplemental Indenture, dated as of September 23, 2019, the Eighteenth Supplemental Indenture, dated as of September 23, 2019, the Nineteenth Supplemental Indenture, dated as of September 23, 2019, the Twentieth Supplemental Indenture, dated as of September 23, 2019, the Twenty-First Supplemental Indenture, dated as of September 23, 2019, the Twenty-Second Supplemental Indenture, dated as of September 23, 2019, the Twenty-Third Supplemental Indenture, dated as of August 18, 2020, the Twenty-Fourth Supplemental Indenture, dated as of August 18, 2020, the Twenty-Fifth Supplemental Indenture, dated as of March 14, 2022, the Twenty-Sixth Supplemental Indenture, dated as of August 11, 2022, the Twenty-Seventh Supplemental Indenture, dated as of February 9, 2023 and the Twenty-Eighth Supplemental Indenture, dated as of February 9, 2023 (as so supplemented, the “Base Indenture”), in each case, between the Partnership and The Bank of New York Mellon Trust Company, N.A., as Trustee (the “Trustee”). Certain terms of the Securities will be established pursuant to one or more supplemental indentures (each, a “Supplemental Indenture”) delivered pursuant to the Base Indenture (such Supplemental Indentures, together with the Base Indenture, the “Indenture”).

The Partnership has filed with the Securities and Exchange Commission (the “Commission”) a registration statement on Form S-3 (the file number of which is set forth in Schedule I hereto), including a prospectus relating to securities (the “Shelf Securities”), including the Securities, to be issued from time to time thereunder by the Partnership. The registration statement as amended to the date of this Agreement,

including the information (if any) deemed to be part of the registration statement at the time of effectiveness pursuant to Rule 430A or Rule 430B under the Securities Act of 1933, as amended (the “Securities Act”), is hereinafter referred to as the “Registration Statement,” and the related prospectus covering the Shelf Securities dated May 15, 2023 in the form first used to confirm sales of the Securities (or in the form first made available to the Underwriters by the Partnership to meet requests of purchasers pursuant to Rule 173 under the Securities Act) is hereinafter referred to as the “Basic Prospectus.” The Basic Prospectus, as supplemented by the prospectus supplement specifically relating to the Securities in the form first used to confirm sales of the Securities (or in the form first made available to the Underwriters by the Partnership to meet requests of purchasers pursuant to Rule 173 under the Securities Act) is hereinafter referred to as the “Prospectus,” and the term “preliminary prospectus” means any preliminary form of the Prospectus. For purposes of this Agreement, “free writing prospectus” has the meaning set forth in Rule 405 under the Securities Act, “Time of Sale Prospectus” means the documents set forth opposite the caption “Time of Sale Prospectus” in Schedule I hereto. As used herein, the terms “Registration Statement,” “Basic Prospectus,” “preliminary prospectus,” “Time of Sale Prospectus” and “Prospectus” shall include the documents incorporated by reference therein (the “Incorporated Documents”). The terms “supplement,” “amendment,” and “amend” as used herein with respect to the Registration Statement, the Basic Prospectus, the Time of Sale Prospectus, any preliminary prospectus or the Prospectus shall include all documents subsequently filed by the Partnership with the Commission pursuant to the Securities Exchange Act of 1934, as amended (the “Exchange Act”), that are deemed to be incorporated by reference therein. “Time of Sale” means 4:00 p.m. (New York City time) on the date of this Agreement.

1. Representations and Warranties. The Partnership and MPLX GP LLC, a Delaware limited liability company (the “General Partner”), jointly and severally represent and warrant to, and agree with, you that:

(a) The Registration Statement has become effective under the Securities Act; no stop order suspending the effectiveness of the Registration Statement under the Securities Act is in effect, and no proceedings for such purpose are pending before or, to the knowledge of the Partnership or the General Partner, threatened by the Commission. The Registration Statement is an automatic shelf registration statement as defined in Rule 405 under the Securities Act and the Partnership is a well-known seasoned issuer (as defined in Rule 405 under the Securities Act) eligible to use the Registration Statement as an automatic shelf registration statement, and the Partnership has not received notice that the Commission objects to the use of the Registration Statement as an automatic shelf registration statement.

(b) (i) Each document, if any, filed or to be filed pursuant to the Exchange Act and incorporated by reference in the Registration Statement, the Time of Sale Prospectus or the Prospectus complied or will comply, as the case may be, when so filed in all material respects

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with the Exchange Act and the applicable rules and regulations of the Commission thereunder, (ii) each part of the Registration Statement, when such part became effective, did not contain, and each such part, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (iii) the Registration Statement as of the date hereof does not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (iv) the Registration Statement, as of the date hereof, complies, and the Prospectus, as of its date, will comply, and the Registration Statement and the Prospectus, as amended or supplemented, if applicable, will comply, as of the Closing Date (as defined in Section 4), in all material respects with the Securities Act and the applicable rules and regulations of the Commission thereunder, (v) the Time of Sale Prospectus does not, and at the time of each sale of the Securities in connection with the offering when the Prospectus is not yet available to prospective purchasers and at the Closing Date, the Time of Sale Prospectus, as then amended or supplemented by the Partnership, if applicable, will not, contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, (vi) each free writing prospectus (including any electronic roadshow), when considered together with the Time of Sale Prospectus, does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading and (vii) the Prospectus does not contain and, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, except that the representations and warranties set forth in this paragraph do not apply to statements or omissions in the Registration Statement, the Time of Sale Prospectus or the Prospectus based upon information relating to any Underwriter furnished to the Partnership in writing by such Underwriter through the Representatives expressly for use therein.

(c) The Partnership is not an “ineligible issuer” in connection with the offering of the Securities pursuant to Rules 164, 405 and 433 under the Securities Act. Any free writing prospectus that the Partnership is required to file pursuant to Rule 433(d) under the Securities Act has been, or will be, filed with the Commission in accordance with the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder. Each free writing prospectus that the Partnership has filed, or is required to file, in connection with the offering of the Securities pursuant to

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Rule 433(d) under the Securities Act or that was prepared by or on behalf of or used or referred to by the Partnership complies or will comply in all material respects with the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder. Except for the free writing prospectuses, if any, identified in Schedule I hereto, and electronic road shows, if any, each furnished to you before first use, the Partnership has not prepared, used or referred to, and will not, without your prior consent, prepare, use or refer to, any free writing prospectus.

(d) Each of the Partnership and the General Partner has been duly formed, is validly existing as a limited partnership or a limited liability company, as the case may be, in good standing under the laws of the State of Delaware, has the limited partnership or limited liability company, as the case may be, power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus and the Prospectus and, with respect to the General Partner, to act as the general partner of the Partnership, and is duly qualified to transact business and is in good standing in each jurisdiction in which the conduct of its business or its ownership or leasing of property requires such qualification, except to the extent that the failure to be so qualified or be in good standing would not have a material adverse effect on the consolidated financial position or results of operations of the Partnership and its subsidiaries, as that term is defined in Rule 405 under the Securities Act (the “Subsidiaries,” and individually, a “Subsidiary”), taken as a whole (a “Material Adverse Effect”).

(e) The General Partner is the sole general partner of the Partnership; the General Partner owns a general partner interest in the Partnership; such general partner interest is duly authorized by the Sixth Amended and Restated Agreement of Limited Partnership of the Partnership (the “Partnership Agreement”), and was validly issued to or acquired by the General Partner and the General Partner owns such general partner interest free and clear of any lien, encumbrance, security interest, equity or charge (except for such liens, encumbrances, security interests, equities or charges as are not, individually or in the aggregate, material to such ownership).

(f) Each Subsidiary of the Partnership which is a significant subsidiary as defined in Rule 1-02(w) of Regulation S-X (as of December 31, 2023 (each a “Significant Subsidiary”)) (x) has been duly formed and is validly existing in good standing under the laws of the jurisdiction of its formation, (y) has the corporate, limited liability company, limited partnership, partnership or other entity power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus and the Prospectus and (z) is duly qualified to transact business and is in good standing in each jurisdiction in which

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the conduct of its business or its ownership or leasing of property requires such qualification, except to the extent that the failure to be so qualified or be in good standing would not have a Material Adverse Effect.

(g) This Agreement has been duly authorized, executed and delivered by, and is a valid and binding instrument of the Partnership and the General Partner.

(h) The Partnership Agreement has been duly authorized, executed and delivered by, and is a valid and binding instrument of, the General Partner, enforceable against the General Partner in accordance with its terms, except as the enforceability thereof is subject to the effects of (i) any applicable bankruptcy, insolvency, reorganization, moratorium, fraudulent conveyance or transfer or other laws relating to or affecting creditors’ rights generally, (ii) general principles of equity (regardless of whether such enforceability is considered in a proceeding in equity or at law) and (iii) any implied covenants of good faith and fair dealing.

(i) The Securities have been duly authorized and, when executed and authenticated in accordance with the provisions of the Indenture and delivered to and paid for by the Underwriters in accordance with the terms of this Agreement, will be valid and binding obligations of the Partnership, in each case enforceable against the Partnership in accordance with their respective terms, except as the enforceability thereof is subject to the effects of (i) any applicable bankruptcy, insolvency, reorganization, moratorium, fraudulent conveyance or transfer or other laws relating to or affecting creditors’ rights generally, (ii) general principles of equity (regardless of whether such enforceability is considered in a proceeding in equity or at law) and (iii) any implied covenants of good faith and fair dealing; the Securities will be entitled to the benefits of the Indenture, and the Securities and the Indenture will conform in all material respects to the respective descriptions thereof in the Time of Sale Prospectus and the Prospectus.

(j) The Base Indenture has been duly qualified under the Trust Indenture Act of 1939, as amended, and each of the Base Indenture and each Supplemental Indenture has been duly authorized and, on the Closing Date, will have been duly executed and delivered by, and thereupon, after execution thereof by the Trustee, the Indenture will be a valid and binding instrument of the Partnership, enforceable against the Partnership in accordance with its terms, except as the enforceability thereof is subject to the effects of (i) any applicable bankruptcy, insolvency, reorganization, moratorium, fraudulent conveyance or transfer or other laws relating to or affecting creditors’ rights generally, (ii) general principles of equity (regardless of whether such

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enforceability is considered in a proceeding in equity or at law) and (iii) any implied covenants of good faith and fair dealing.

(k) The execution and delivery by the Partnership and the General Partner of, and the performance by each of the Partnership and the General Partner of its obligations under, this Agreement, the Indenture and the Securities, as applicable, will not contravene any provision of applicable law, the certificate of formation or the limited liability company agreement of the General Partner, the certificate of limited partnership or the Partnership Agreement of the Partnership or any agreement, indenture or other instrument binding upon the Partnership, the General Partner or their respective Subsidiaries that is material to the Partnership and its Subsidiaries, taken as a whole, or any judgment, order or decree of any governmental body, agency or court having jurisdiction over the Partnership, the General Partner or the Significant Subsidiaries, and no consent, approval, authorization or order of, or qualification with, any governmental body or agency that has not already been obtained is required for the performance by the Partnership or the General Partner of its obligations under this Agreement, the Indenture or the Securities, except such as may be required by the securities or Blue Sky laws of the various states in connection with the offer and sale of the Securities.

(l) None of the Partnership, the General Partner or any of the Partnership’s Subsidiaries is in violation of its certificate of formation, certificate of limited partnership or other constitutive document or in default under any agreement, indenture or instrument, which default could reasonably be expected to have a Material Adverse Effect and no event or condition has occurred or exists which, with the giving of notice or the lapse of time or both, would result in any such violation or default which could reasonably be expected to have a Material Adverse Effect. Except as described in the Time of Sale Prospectus and the Prospectus, none of the Partnership, the General Partner or any of the Partnership’s Subsidiaries is in violation of any law, ordinance, governmental rule or regulation or court decree to which it may be subject, which violation could reasonably be expected to have a Material Adverse Effect.

(m) There has not occurred any material adverse change, or any development involving a material adverse change, in the condition, financial or otherwise, or in the earnings, business or operations of the Partnership and its Subsidiaries, taken as a whole, from that set forth in the Time of Sale Prospectus and the Prospectus.

(n) There are no legal or governmental investigations or proceedings pending or, to the knowledge of the Partnership or the General Partner, threatened to which the Partnership, the General Partner or any of the Partnership’s Subsidiaries is a party or to which any of the

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properties of the Partnership, the General Partner or any of the Partnership’s Subsidiaries is subject, that would be required to be described in the Registration Statement, the Time of Sale Prospectus or the Prospectus and are not so described or any statutes, regulations, contracts or other documents that would be required to be described in the Registration Statement, the Time of Sale Prospectus or the Prospectus or to be filed as exhibits to the Registration Statement that are not described or filed as required.

(o) To the Partnership’s and the General Partner’s knowledge, PricewaterhouseCoopers LLP, which has certified the financial statements of the Partnership and its consolidated Subsidiaries and delivered its report with respect to the audited consolidated financial statements and schedules included or incorporated by reference in the Registration Statement, the Time of Sale Prospectus and the Prospectus, is an independent public accountant with respect to the Partnership within the meaning of the Securities Act.

(p) Each preliminary prospectus filed as part of the Registration Statement as originally filed or as part of any amendment thereto, or filed pursuant to Rule 424 under the Securities Act, complied when so filed in all material respects with the Securities Act and the applicable rules and regulations of the Commission thereunder.

(q) Neither the Partnership nor the General Partner is, nor immediately after giving effect to the offering and sale of the Securities and the application of the proceeds thereof as described in the Time of Sale Prospectus and the Prospectus will be, required to register as an “investment company” as such term is defined in the Investment Company Act of 1940, as amended.

(r) The Partnership and its Subsidiaries (i) are in compliance with all applicable foreign, federal, state and local laws and regulations relating to the protection of human health and safety (with respect to hazardous or toxic substances) or the environment, including with respect to releases of hazardous or toxic substances or wastes, pollutants or contaminants (“Environmental Laws”), (ii) possess all permits, licenses or other approvals required of them under applicable Environmental Laws to conduct their respective businesses and (iii) are in compliance with all terms and conditions of any such permit, license or approval, except where such noncompliance with Environmental Laws, failure to receive required permits, licenses or other approvals or failure to comply with the terms and conditions of such permits, licenses or approvals would not, singly or in the aggregate, reasonably be expected to have a Material Adverse Effect.

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(s) None of the Partnership, the General Partner or any of the Partnership’s Subsidiaries or, to the knowledge of the Partnership or the General Partner, any director, officer, agent, employee or affiliate of the Partnership or the General Partner or any of the Partnership’s Subsidiaries is aware of or has taken any action, directly or indirectly, that would result in a violation or a sanction for violation by such persons of the Foreign Corrupt Practices Act of 1977 or the U.K. Bribery Act 2010, each as may be amended, or similar law of any other jurisdiction in which the Partnership or the General Partner and the Partnership’s Subsidiaries conduct business, or the rules and regulations thereunder; and the Partnership, the General Partner and the Partnership’s Subsidiaries have instituted and maintain policies and procedures designed to ensure compliance therewith. No part of the proceeds of the offering will be used, directly or indirectly, in violation of the Foreign Corrupt Practices Act of 1977 or the U.K. Bribery Act of 2010, each as may be amended, or similar law of any other jurisdiction in which the Partnership, the General Partner and the Partnership’s Subsidiaries conduct business, or the rules and regulations thereunder.

(t) The operations of the Partnership, General Partner and the Partnership’s Subsidiaries are and have been conducted at all times in compliance in all material respects with all applicable financial recordkeeping and reporting requirements, including those of the Bank Secrecy Act, as amended by Title III of the Uniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism Act of 2001 (USA PATRIOT Act), and the applicable anti-money laundering statutes of jurisdictions where the Partnership, the General Partner and the Partnership’s Subsidiaries conduct business, the rules and regulations thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any governmental agency (collectively, the “Anti-Money Laundering Laws”), and no action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Partnership, the General Partner or any of the Partnership’s Subsidiaries with respect to the Anti-Money Laundering Laws is pending or, to the knowledge of the Partnership or the General Partner, threatened.

(u) (i) None of the Partnership, the General Partner or any of the Partnership’s Subsidiaries, or to the Partnership’s or General Partner’s knowledge, any director, officer, employee, agent, affiliate or representative of the Partnership or the General Partner or any of the Partnership’s Subsidiaries, is an individual or entity (“Person”) that is, or is owned or controlled by a Person that is:

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(A) the subject of any sanctions administered or enforced by the U.S. Department of Treasury’s Office of Foreign Assets Control or other relevant sanctions authority (collectively, “Sanctions”), nor

(B) located, organized or resident in a country or territory that is the subject of Sanctions (including, without limitation, the so-called Donetsk People’s Republic, the so-called Luhansk People’s Republic, the non-government controlled areas of the Zaporizhzhia and Kherson Regions of Ukraine, the Crimea region of Ukraine and other Covered Regions (as defined in the Executive Order 14065) of Ukraine identified pursuant to the Executive Order 14065, Cuba, Iran, North Korea and Syria).

(ii) Neither the Partnership nor the General Partner will, directly or indirectly, use the proceeds of the offering, or lend, contribute or otherwise make available such proceeds to any Subsidiary, joint venture partner or other Person:

(A) to fund or facilitate any activities or business of or with any Person or in any country or territory that, at the time of such funding or facilitation, is the subject of Sanctions; or

(B) in any other manner that will result in a violation of Sanctions by any Person (including any Person participating in the offering, whether as underwriter, advisor, investor or otherwise).

(iii) The Partnership, the General Partner and the Partnership’s Subsidiaries have not knowingly engaged in, are not now knowingly engaged in, and will not knowingly engage in, any dealings or transactions with any Person, or in any country or territory, that at the time of the dealing or transaction is or was the subject of Sanctions.

(v) The Partnership and each of its Subsidiaries have filed all federal, state, local and foreign tax returns required to be filed through the date of this Agreement or have requested extensions thereof and have paid all taxes required to be paid thereon (except where the failure to file or pay could not reasonably be expected to have a Material Adverse Effect, or, except as currently being contested in good faith and for which adequate reserves required by U.S. generally accepted accounting principles (“U.S. GAAP”) have been created in the financial statements of the Partnership), and no tax deficiency has been determined adversely to the Partnership or any of its Subsidiaries which has had (nor does the Partnership nor any of its Subsidiaries have any notice or knowledge of any tax deficiency which could reasonably be expected to be determined adversely to the Partnership or its Subsidiaries and which could reasonably be expected to have) a Material Adverse Effect (except as currently being contested in good faith and for

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which adequate reserves required by U.S. GAAP have been created in the financial statements of the Partnership).

(w) The Partnership and its Subsidiaries, taken as a whole, maintain a system of internal accounting controls sufficient to provide reasonable assurance that (i) transactions are executed in accordance with management’s general or specific authorizations; (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with U.S. GAAP and to maintain asset accountability; (iii) access to assets is permitted only in accordance with management’s general or specific authorization; and (iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences. Except as described in the Time of Sale Prospectus and the Prospectus, since the end of the Partnership’s most recent audited fiscal year, there has been (i) no material weakness in the Partnership’s internal control over financial reporting (whether or not remediated) and (ii) no change in the Partnership’s internal control over financial reporting that has materially affected, or is reasonably likely to materially affect, the Partnership’s internal control over financial reporting.

(x) The interactive data in eXtensible Business Reporting Language or Inline eXtensible Business Reporting Language included or incorporated by reference in the Registration Statement and the Prospectus fairly presents the information called for in all material respects and has been prepared in all material respects in accordance with the Commission’s rules and guidelines applicable thereto.

2. Agreements to Sell and Purchase. The Partnership hereby agrees to sell to the several Underwriters, and each Underwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from the Partnership the respective principal amounts of Securities set forth in Schedule II hereto opposite its name at the purchase price for the Securities set forth in Schedule I hereto.

3. Public Offering. You have advised the Partnership that the Underwriters propose to make a public offering of the Securities purchased by the Underwriters hereunder as soon as practicable after the execution and delivery of this Agreement.

4. Payment and Delivery. Payment for the Securities shall be made to the Partnership in Federal or other funds immediately available in New York City on the closing date and time set forth in Schedule I hereto, or at such other time on the same or such other date, not later than the third business day thereafter, as may be designated in writing by you. The time and date of such payment are hereinafter referred to as the “Closing Date.”

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Payment for the Securities shall be made against delivery to you on the Closing Date for the respective accounts of the several Underwriters of the Securities registered in such names and in such denominations as you shall request in writing not later than one full business day prior to the Closing Date, with any transfer taxes payable in connection with the transfer of the Securities to the Underwriters duly paid.

5. Conditions to the Underwriters’ Obligations. The several obligations of the Underwriters to purchase and pay for the Securities on the Closing Date are subject to the following conditions:

(a) The representations and warranties of the Partnership and the General Partner contained herein are true and correct on the date hereof, as of the Time of Sale and as of the Closing Date, and each of the Partnership and the General Partner shall have complied with all agreements and all conditions on its part to be performed or satisfied hereunder at or prior to the Closing Date.

(b) Subsequent to the execution and delivery of this Agreement and prior to the Closing Date there shall not have occurred any downgrading, nor shall any notice have been given of any intended or potential downgrading or of any review, with possible negative implications, of the rating accorded any of the debt securities of the Partnership by any “nationally recognized statistical rating organization,” as such term is defined in Section 3(a)(62) of the Exchange Act.

(c) Since the respective dates as of which information is given in the Time of Sale Prospectus, there shall not have been any material change in the partnership interests in the Partnership or the long-term debt of the Partnership or any of its Subsidiaries or any material adverse change, or any development involving a prospective material adverse change, in or affecting the general affairs, business, financial position, equity or results of operations of the Partnership and its Subsidiaries, taken as a whole, otherwise than as set forth or contemplated in the Time of Sale Prospectus and the Prospectus (exclusive of any amendments or supplements thereto subsequent to the date of this Agreement), the effect of which in the judgment of the Representatives makes it impracticable or inadvisable to proceed with the offering or the delivery of the Securities on the terms and in the manner contemplated in the Time of Sale Prospectus and the Prospectus.

(d) The Representatives shall have received on and as of the Closing Date a certificate of an officer of the General Partner reasonably satisfactory to you with respect to the matters set forth in Sections 5(a) and 5(b) and to the further effect that there has not occurred any material adverse change, or any development involving a prospective material adverse change, in or affecting the general affairs, business, financial

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position, equity or results of operations of the Partnership and its Subsidiaries, taken as a whole, otherwise than as set forth or contemplated in the Time of Sale Prospectus and the Prospectus.

(e) The Underwriters shall have received on the Closing Date an opinion of Jones Day, outside counsel for the Partnership and the General Partner, dated the Closing Date, in form and substance reasonably satisfactory to the Underwriters.

(f) The Underwriters shall have received on the Closing Date an opinion of Richards, Layton & Finger, P.A., special Delaware counsel for the Partnership and the General Partner, dated the Closing Date, in form and substance reasonably satisfactory to the Underwriters.

(g) The Underwriters shall have received on the Closing Date an opinion of Cravath, Swaine & Moore LLP, counsel for the Underwriters, dated the Closing Date, in form and substance reasonably satisfactory to the Underwriters.

(h) On the date of this Agreement and on the Closing Date, PricewaterhouseCoopers LLP shall have furnished to you letters dated such dates, in form and substance reasonably satisfactory to the Underwriters and PricewaterhouseCoopers LLP, containing statements and information of the type customarily included in accountants’ “comfort letters” to underwriters with respect to the financial statements and certain financial information contained in or incorporated by reference into the Registration Statement, the Time of Sale Prospectus and the Prospectus relating to the Partnership; provided that the letter delivered on the Closing Date shall use a “cut-off” date no more than three business days prior to such Closing Date.

6. Covenants of the Partnership and the General Partner. The Partnership and the General Partner jointly and severally covenant with each Underwriter as follows:

(a) To furnish to you in New York City, without charge, prior to 10:00 a.m. New York City time on the business day next succeeding the date of this Agreement, a signed copy (which may be electronic) of the Registration Statement (without exhibits thereto) and to deliver to each of the Underwriters during the period mentioned in Section 6(e) or 6(f) below, as many copies of the Time of Sale Prospectus, the Prospectus and any supplements and amendments thereto or to the Registration Statement as you may reasonably request.

(b) From the date hereof to the Closing Date, before amending or supplementing the Registration Statement, the Time of Sale Prospectus or the Prospectus, to furnish to you a copy of each such proposed amendment or supplement and, unless such filing is required

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under applicable laws and regulations, not to file any such proposed amendment or supplement to which you reasonably object.

(c) From the date hereof to the Closing Date, to furnish to you a copy of each proposed free writing prospectus to be prepared by or on behalf of, used by, or referred to by the Partnership or the General Partner and not to use or refer to any proposed free writing prospectus to which you reasonably object.

(d) Not to take any action that would result in an Underwriter, the Partnership or the General Partner being required to file with the Commission pursuant to Rule 433(d) under the Securities Act a free writing prospectus prepared by or on behalf of the Underwriter that the Underwriter otherwise would not have been required to file thereunder.

(e) If the Time of Sale Prospectus is being used to solicit offers to buy the Securities at a time when the Prospectus is not yet available to prospective purchasers and any event shall occur or condition shall exist as a result of which it is necessary to amend or supplement the Time of Sale Prospectus in order to make the statements therein, in the light of the circumstances at the time of such delivery, not misleading, or if, in the reasonable opinion of counsel for the Underwriters, it is necessary to amend or supplement the Time of Sale Prospectus to comply with applicable law, forthwith to prepare, file with the Commission and furnish, at its own expense, to the Underwriters and to any dealer upon request, either amendments or supplements to the Time of Sale Prospectus so that the statements in the Time of Sale Prospectus as so amended or supplemented will not, in the light of the circumstances when the Time of Sale Prospectus is delivered to a prospective purchaser, be misleading, or so that the Time of Sale Prospectus, as amended or supplemented, will comply with applicable law.

(f) If, during such period after the first date of the public offering of the Securities as in the reasonable opinion of counsel for the Underwriters the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) under the Securities Act) is required by law to be delivered in connection with sales by an Underwriter or dealer, any event shall occur or condition shall exist as a result of which it is necessary to amend or supplement the Prospectus in order to make the statements therein, in the light of the circumstances when the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) under the Securities Act) is delivered to a purchaser, not misleading, or if it is necessary to amend or supplement the Prospectus to comply with applicable law, forthwith to prepare, file with the Commission and furnish, at its own expense, to the Underwriters, either amendments or supplements to the Prospectus so that the statements in the Prospectus as so amended or supplemented will not, in the light of the circumstances when the Prospectus (or in lieu

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thereof the notice referred to in Rule 173(a) under the Securities Act) is delivered to a purchaser, be misleading or so that the Prospectus, as amended or supplemented, will comply with applicable law.

(g) To endeavor to qualify the Securities for offer and sale under the securities or Blue Sky laws of such jurisdictions as you shall reasonably request and to continue such qualification in effect so long as reasonably required for distribution of the Securities; provided that in connection therewith neither the Partnership nor the General Partner shall be required to qualify as a foreign corporation or to file a general consent to service of process in any jurisdiction or to subject itself to taxation in any jurisdiction.

(h) During the period beginning on the date hereof and continuing to and including the business day following the Closing Date, not to offer, sell, contract to sell or otherwise dispose of any debt securities of or guaranteed by the Partnership which are substantially similar to the Securities.

(i) To use the net proceeds received by the Partnership from the sale of the Securities pursuant to this Agreement in the manner specified in the Time of Sale Prospectus and the Prospectus under the caption “Use of Proceeds”.

(j) To make generally available to the Partnership’s securityholders and to you as soon as practicable an earnings statement covering a period of at least twelve months beginning with the first fiscal quarter of the Partnership occurring after the date of this Agreement which shall satisfy the provisions of Section 11(a) of the Securities Act and the rules and regulations of the Commission thereunder.

(k) Whether or not the transactions contemplated in this Agreement are consummated or this Agreement is terminated, to pay or cause to be paid all costs and expenses incident to the performance of its obligations hereunder, including without limiting the generality of the foregoing, all costs and expenses (including reasonable fees and expenses of the Partnership’s and the General Partner’s counsel and accountants) (i) incident to the preparation, issuance, execution, authentication and delivery of the Securities, including any expenses of the Trustee, and any taxes payable by the Partnership or the General Partner in connection therewith, (ii) incident to the preparation and filing of the Registration Statement, any preliminary prospectus, the Time of Sale Prospectus, the Prospectus, any free writing prospectus prepared by or on behalf of, used by, or referred to by the Partnership or the General Partner (including in each case all exhibits, amendments and supplements to any of the foregoing, including the filing fees payable to

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the Commission relating to the Securities (within the time required by Rule 456(b)(1) under the Securities Act, if applicable), all printing costs associated therewith, and the mailing and delivering of copies thereof to the Underwriters and dealers, in the quantities hereinabove specified), (iii) incurred in connection with the registration or qualification and determination of eligibility for investment of the Securities under the laws of such jurisdictions as the Underwriters may designate (including reasonable fees and disbursements of counsel for the Underwriters associated therewith, which fees and expenses shall not exceed $10,000), (iv) incurred in connection with the printing (including word processing and duplication costs) and delivery of this Agreement, the Indenture, any Blue Sky memoranda relating to the offer and sale of the Securities and the furnishing to Underwriters of copies of the Registration Statement, any preliminary prospectus, the Time of Sale Prospectus and the Prospectus, including mailing and shipping, as herein provided, (v) payable to the Underwriters incurred in connection with the review and qualification of the offering of the Securities by the Financial Industry Regulatory Authority, if applicable, (vi) payable to the rating agencies in connection with the rating of the Securities and (vii) incurred by the Partnership or the General Partner in connection with a “road show” presentation to potential investors. For the avoidance of doubt, except as provided in this Section, Section 8 entitled “Indemnity and Contribution” and the last paragraph of Section 10, the Underwriters will pay all of their costs and expenses, including fees and disbursements of their counsel and any advertising expenses connected with any offers they may make.

(l) To prepare a final term sheet relating to the offering of the Securities, containing only information that describes the final terms of the Securities or the offering in a form consented to by the Representatives, and to file such final term sheet within the period required by Rule 433(d)(5)(ii) under the Securities Act on or following the date the final terms have been established for the offering of the Securities.

(m) Not to take any action prohibited by Regulation M under the Exchange Act in connection with the distribution of the Securities contemplated hereby.

(n) To pay the required Commission filing fees relating to the Securities within the time required by Rule 456(b)(1) under the Securities Act without regard to the proviso therein and otherwise in accordance with Rules 456(b) and 457(r) under the Securities Act.

7. Covenants of the Underwriters. Each Underwriter covenants with the Partnership and the General Partner not to take any action that would result in the Partnership being required to file with the Commission under Rule 433(d) under the

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Securities Act a free writing prospectus prepared by or on behalf of such Underwriter that otherwise would not be required to be filed thereunder, but for the action of such Underwriter.

8. Indemnity and Contribution. (a) The Partnership and the General Partner agree, jointly and severally, to indemnify and hold harmless each Underwriter, the directors, officers and employees of each Underwriter, and each person, if any, who controls any Underwriter within the meaning of either Section 15 of the Securities Act or Section 20 of the Exchange Act and each affiliate of any Underwriter within the meaning of Rule 405 under the Securities Act from and against any and all losses, claims, damages and liabilities (including, without limitation, any out-of-pocket legal fees or other expense reasonably incurred in connection with defending or investigating any such action or claim) (i) caused by any untrue statement or alleged untrue statement of a material fact contained in the Registration Statement or any amendment thereof, or caused by any omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading or (ii) caused by any untrue statement or alleged untrue statement of a material fact contained in any preliminary prospectus, the Time of Sale Prospectus or any amendment or supplement thereto, any issuer free writing prospectus as defined in Rule 433(h) under the Securities Act (including any electronic roadshow), any Partnership or General Partner information that the Partnership or the General Partner has filed, or is required to file, pursuant to Rule 433(d) under the Securities Act, or the Prospectus or any amendment or supplement thereto, or caused by any omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, except, in each case, insofar as such losses, claims, damages or liabilities are caused by any such untrue statement or omission or alleged untrue statement or omission based upon information relating to any Underwriter furnished to the Partnership or the General Partner in writing by any Underwriter through you expressly for use therein.

(b) Each Underwriter agrees, severally and not jointly, to indemnify and hold harmless the Partnership and the General Partner and their respective directors, their respective officers who sign the Registration Statement and each person, if any, who controls the Partnership or the General Partner within the meaning of either Section 15 of the Securities Act or Section 20 of the Exchange Act to the same extent as the foregoing indemnity from the Partnership and the General Partner to such Underwriter, but only to the extent that such untrue statement or omission or alleged untrue statement or omission was made in the Registration Statement, any preliminary prospectus, the Time of Sale Prospectus, any issuer free writing prospectus (including any electronic roadshow) or the Prospectus or any amendment or supplement thereto in reliance upon and in conformity with written information furnished to the Partnership or the General Partner by such Underwriter through you expressly for use therein; and will reimburse the Partnership and the General Partner for any out-of-pocket legal fees or other expense reasonably incurred by the Partnership or the General

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Partner in connection with investigating or defending any such action or claim.

(c) In case any suit, action, proceeding (including any governmental or regulatory investigation), claim or demand shall be instituted involving any person in respect of which indemnity may be sought pursuant to Section 8(a) or 8(b), such person (the “indemnified party”) shall promptly notify the person against whom such indemnity may be sought (the “indemnifying party”) in writing and the indemnifying party, upon request of the indemnified party, shall retain counsel reasonably satisfactory to the indemnified party to represent the indemnified party and any others the indemnifying party may designate in such proceeding and shall pay the fees and expenses of such counsel related to such proceeding. In any such proceeding, any indemnified party shall have the right to retain its own counsel, but the fees and expenses of such counsel shall be at the expense of such indemnified party unless (i) the indemnifying party and the indemnified party shall have mutually agreed to the contrary or (ii) the named parties to any such proceeding (including any impleaded parties) include both the indemnifying party and the indemnified party and representation of both parties by the same counsel would be inappropriate due to actual or potential differing interests between them. It is understood that the indemnifying party shall not, in respect of the legal expenses of any indemnified party in connection with any proceeding or related proceedings in the same jurisdiction, be liable for the fees and expenses of more than one separate firm (in addition to any local counsel) for all such indemnified parties and that all such fees and expenses shall be reimbursed as they are incurred. Such firm shall be designated in writing by the Representatives, in the case of parties indemnified pursuant to Section 8(a), and by the Partnership and the General Partner, in the case of parties indemnified pursuant to Section 8(b). The indemnifying party shall not be liable for any settlement of any proceeding effected without its written consent, but if settled with such consent or if there be a final judgment for the plaintiff, the indemnifying party agrees to indemnify the indemnified party from and against any loss or liability by reason of such settlement or judgment. No indemnifying party shall, without the prior written consent of the indemnified party, effect any settlement of any pending or threatened proceeding in respect of which any indemnified party is or could have been a party and indemnity could have been sought hereunder by such indemnified party, unless such settlement (i) includes an unconditional release of such indemnified party from all liability on claims that are the subject matter of such proceeding and (ii) does not include a statement as to or an admission of fault, culpability or failure to act, by or on behalf of any indemnified party.

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(d) To the extent the indemnification provided for in Section 8(a) or 8(b) is unavailable to an indemnified party or insufficient in respect of any losses, claims, damages or liabilities referred to therein, then each indemnifying party under such paragraph, in lieu of indemnifying such indemnified party thereunder, shall contribute to the amount paid or payable by such indemnified party as a result of such losses, claims, damages or liabilities (i) in such proportion as is appropriate to reflect the relative benefits received by the Partnership and the General Partner on the one hand and the Underwriters on the other hand from the offering of the Securities or (ii) if the allocation provided by clause (d)(i) above is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (d)(i) above but also the relative fault of the Partnership and the General Partner on the one hand and of the Underwriters on the other hand in connection with the statements or omissions that resulted in such losses, claims, damages or liabilities, as well as any other relevant equitable considerations. The relative benefits received by the Partnership and the General Partner on the one hand and the Underwriters on the other hand in connection with the offering of the Securities shall be deemed to be in the same respective proportions as the net proceeds from the offering of the Securities (before deducting expenses) received by the Partnership and the General Partner and the total underwriting discounts and commissions received by the Underwriters bear to the aggregate initial public offering price of the Securities as set forth in the Prospectus. The relative fault of the Partnership and the General Partner on the one hand and the Underwriters on the other hand shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Partnership and the General Partner or by the Underwriters and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission. The Underwriters’ respective obligations to contribute pursuant to this Section 8 are several in proportion to the respective principal amount of Securities they have purchased hereunder, and not joint.

(e) The Partnership and the General Partner and the Underwriters agree that it would not be just or equitable if contribution pursuant to this Section 8 were determined by pro rata allocation (even if the Underwriters were treated as one entity for such purpose) or by any other method of allocation that does not take account of the equitable considerations referred to in Section 8(d). The amount paid or payable by an indemnified party as a result of the losses, claims, damages and liabilities referred to in Section 8(d) shall be deemed to include, subject to the limitations set forth above, any legal or other expenses reasonably incurred by such indemnified party in connection

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with investigating or defending any such action or claim. Notwithstanding the provisions of this Section , no Underwriter shall be required to contribute any amount in excess of the amount by which the total price at which the Securities underwritten by it and distributed to the public were offered to the public exceeds the amount of any damages that such Underwriter has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The remedies provided for in this Section 8 are not exclusive and shall not limit any rights or remedies which may otherwise be available to any indemnified party at law or in equity.

(f) The indemnity and contribution provisions contained in this Section 8 and the representations and warranties of the Partnership and the General Partner contained in this Agreement shall remain operative and in full force and effect regardless of (i) any termination of this Agreement, (ii) any investigation made by or on behalf of any Underwriter, any person controlling any Underwriter or by or on behalf of the Partnership, the General Partner, their respective officers or directors or any person controlling the Partnership or the General Partner and (iii) acceptance of and payment for any of the Securities.

9. Termination. The Underwriters may terminate this Agreement by notice given by you to the Partnership, if after the execution and delivery of this Agreement and prior to the Closing Date (a) trading generally shall have been suspended or materially limited on, or by, as the case may be, the New York Stock Exchange, (b) trading of any securities of the Partnership shall have been suspended on any exchange or in any over-the-counter market, (c) a general moratorium on commercial banking activities in New York shall have been declared by Federal or New York State authorities or (d) there shall have occurred (i) any outbreak or escalation of hostilities, or any change in financial markets or any calamity or crisis or (ii) a material disruption in securities settlement, payment or clearance services in the United States or other relevant jurisdiction shall have occurred that, in your judgment, is material and adverse and which, singly or together with any other event specified in this clause (d), makes it, in your judgment, impracticable or inadvisable to proceed with the offer, sale or delivery of the Securities on the terms and in the manner contemplated in the Time of Sale Prospectus or the Prospectus.

10. Effectiveness; Defaulting Underwriters. This Agreement shall become effective upon the execution and delivery hereof by the parties hereto.

If, on the Closing Date, any one or more of the Underwriters shall fail or refuse to purchase Securities that it or they have agreed to purchase hereunder on such date, and the aggregate principal amount of Securities which such defaulting Underwriter or Underwriters agreed but failed or refused to purchase is not more than one tenth of the

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aggregate principal amount of the Securities to be purchased on such date, the other Underwriters shall be obligated severally in the proportions that the principal amount of Securities set forth opposite their respective names in Schedule II bears to the aggregate principal amount of Securities set forth opposite the names of all such non-defaulting Underwriters, or in such other proportions as the Representatives may specify, to purchase the Securities which such defaulting Underwriter or Underwriters agreed but failed or refused to purchase on such date; provided that in no event shall the principal amount of Securities that any Underwriter has agreed to purchase pursuant to this Agreement be increased pursuant to this Section 10 by an amount in excess of one tenth of such principal amount of Securities without the written consent of such Underwriter. If, on the Closing Date, any Underwriter or Underwriters shall fail or refuse to purchase Securities which it or they have agreed to purchase hereunder on such date and the aggregate principal amount of Securities with respect to which such default occurs is more than one tenth of the aggregate principal amount of Securities to be purchased on such date, and arrangements reasonably satisfactory to the Representatives, the Partnership and the General Partner for the purchase of such Securities are not made within 36 hours after such default, this Agreement shall terminate without liability on the part of any non-defaulting Underwriter, the Partnership or the General Partner. In any such case either the Representatives, the Partnership or the General Partner shall have the right to postpone the Closing Date, but in no event for longer than seven days, in order that the required changes, if any, in the Registration Statement, in the Time of Sale Prospectus, in the Prospectus or in any other documents or arrangements may be effected. Any action taken under this paragraph shall not relieve any defaulting Underwriter from liability in respect of any default of such Underwriter under this Agreement.

If this Agreement shall be terminated by the Underwriters, or any of them, because of any failure or refusal on the part of the Partnership or the General Partner to comply with the terms or to fulfill any of the conditions of this Agreement, or if for any reason the Partnership or the General Partner shall be unable to perform its obligations under this Agreement other than due to a default by the Underwriters, the Partnership and the General Partner will reimburse the Underwriters or such Underwriters as have so terminated this Agreement with respect to themselves, severally, for all out-of-pocket expenses (including the fees and expenses of their counsel) reasonably incurred by such Underwriters in connection with this Agreement or the offering contemplated hereunder.

11. Entire Agreement. (a) This Agreement represents the entire agreement between the Partnership, the General Partner and the Underwriters with respect to the preparation of any preliminary prospectus, the Time of Sale Prospectus, the Prospectus, the conduct of the offering and the purchase and sale of the Securities.

(b) Each of the Partnership and the General Partner acknowledges that in connection with the offering of the Securities: (i) the Underwriters have acted at arm’s length, are not agents of, and owe no fiduciary duties to, the Partnership, the General Partner or any other person, (ii) the Underwriters owe the Partnership, or the General Partner, only those duties and obligations set forth in this Agreement and (iii) the Underwriters may have interests that differ from those of the

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Partnership and the General Partner. Each of the Partnership and the General Partner waives to the full extent permitted by applicable law any claims it may have against the Underwriters arising from an alleged breach of fiduciary duty in connection with the offering of the Securities.

12. Counterparts. This Agreement may be signed in one or more counterparts, each of which shall constitute an original and all of which together shall constitute one and the same agreement. Counterparts may be delivered via facsimile, electronic mail (including any electronic signature covered by the U.S. federal ESIGN Act or other applicable law, e.g., www.docusign.com) or other transmission method and any counterpart so delivered shall be deemed to have been duly and validly delivered and be valid and effective for all purposes.

13. Applicable Law. This Agreement shall be governed by and construed in accordance with the internal laws of the State of New York, without giving effect to any conflicts of laws provisions thereof that would result in the application of the laws of any other jurisdiction.

14. Headings. The headings of the sections of this Agreement have been inserted for convenience of reference only and shall not be deemed a part of this Agreement.

15. Notices. All communications hereunder shall be in writing and effective only upon receipt and if to the Underwriters shall be delivered, mailed or sent to you c/o the Representatives at the addresses set forth in Schedule I hereto; and if to the Partnership or the General Partner shall be delivered, mailed or sent to their respective address set forth in Schedule I hereto.

In accordance with the requirements of the USA PATRIOT Act (Title III of Pub. L. 107-56 (signed into law October 26, 2001)), the Underwriters are required to obtain, verify and record information that identifies their respective clients, including the Partnership, which information may include the name and address of their respective clients, as well as other information that will allow the Underwriters to properly identify their respective clients.

16. WAIVER OF TRIAL BY JURY. EACH OF THE PARTNERSHIP AND THE GENERAL PARTNER (ON ITS BEHALF AND, TO THE EXTENT PERMITTED BY APPLICABLE LAW, ON BEHALF OF ITS SECURITYHOLDERS AND AFFILIATES) AND EACH OF THE UNDERWRITERS HEREBY IRREVOCABLY WAIVES, TO THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING ARISING OUT OF OR RELATING TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY.

17. Recognition of the U.S. Special Resolution Regime. (a) In the event that any Underwriter that is a Covered Entity becomes subject to a proceeding under a U.S.

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Special Resolution Regime, the transfer from such Underwriter of this Agreement, and any interest and obligation in or under this Agreement, will be effective to the same extent as the transfer would be effective under the U.S. Special Resolution Regime if this Agreement, and any such interest and obligation, were governed by the laws of the United States or a state of the United States.

(b) In the event that any Underwriter that is a Covered Entity or a BHC Act Affiliate of such Underwriter becomes subject to a proceeding under a U.S. Special Resolution Regime, Default Rights under this Agreement that may be exercised against such Underwriter are permitted to be exercised to no greater extent than such Default Rights could be exercised under the U.S. Special Resolution Regime if this Agreement were governed by the laws of the United States or a state of the United States.

As used in this Section 17:

“BHC Act Affiliate” has the meaning assigned to the term “affiliate” in, and shall be interpreted in accordance with, 12 U.S.C. § 1841(k).

“Covered Entity” means any of the following:

(i) a “covered entity” as that term is defined in, and interpreted in accordance with, 12 C.F.R. § 252.82(b);

(ii) a “covered bank” as that term is defined in, and interpreted in accordance with, 12 C.F.R. § 47.3(b); or

(iii) a “covered FSI” as that term is defined in, and interpreted in accordance with, 12 C.F.R. § 382.2(b).

“Default Right” has the meaning assigned to that term in, and shall be interpreted in accordance with, 12 C.F.R. §§ 252.81, 47.2 or 382.1, as applicable.

“U.S. Special Resolution Regime” means each of (i) the Federal Deposit Insurance Act and the regulations promulgated thereunder and (ii) Title II of the Dodd-Frank Wall Street Reform and Consumer Protection Act and the regulations promulgated thereunder.

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Accepted as of the date hereof

Mizuho Securities LLC

RBC Capital Markets, LLC

TD Securities (USA) LLC

Acting severally on behalf of themselves

and the several Underwriters named

in Schedule II hereto

[Signature pages follow]

SCHEDULE I

I-2

Terms applicable to the Senior Notes due 2034 (the “Securities”)

I-3

SCHEDULE II

Exhibit 4.1

EXECUTION VERSION

TWENTY-NINTH SUPPLEMENTAL INDENTURE

THIS TWENTY-NINTH SUPPLEMENTAL INDENTURE, dated as of May 20, 2024 (this “Supplemental Indenture”), is between MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (the “Partnership”), and The Bank of New York Mellon Trust Company, N.A., a national banking association, as trustee (the “Trustee”).

WITNESSETH

WHEREAS, pursuant to the Senior Indenture, dated as of February 12, 2015 (the “Base Indenture”), as supplemented by the First Supplemental Indenture, dated as of February 12, 2015, the Second Supplemental Indenture, dated as of December 22, 2015, the Third Supplemental Indenture, dated as of December 22, 2015, the Fourth Supplemental Indenture, dated as of December 22, 2015, the Fifth Supplemental Indenture, dated as of December 22, 2015, the Sixth Supplemental Indenture, dated as of February 10, 2017, the Seventh Supplemental Indenture, dated as of February 10, 2017, the Eighth Supplemental Indenture, dated as of February 8, 2018, the Ninth Supplemental Indenture, dated as of February 8, 2018, the Tenth Supplemental Indenture, dated as of February 8, 2018, the Eleventh Supplemental Indenture, dated as of February 8, 2018, the Twelfth Supplemental Indenture, dated as of February 8, 2018, the Thirteenth Supplemental Indenture, dated as of November 15, 2018, the Fourteenth Supplemental Indenture, dated as of November 15, 2018, the Fifteenth Supplemental Indenture, dated as of September 9, 2019, the Sixteenth Supplemental Indenture, dated as of September 9, 2019, the Seventeenth Supplemental Indenture, dated as of September 23, 2019, the Eighteenth Supplemental Indenture, dated as of September 23, 2019, the Nineteenth Supplemental Indenture, dated as of September 23, 2019, the Twentieth Supplemental Indenture, dated as of September 23, 2019, the Twenty-First Supplemental Indenture, dated as of September 23, 2019, the Twenty-Second Supplemental Indenture, dated as of September 23, 2019, the Twenty-Third Supplemental Indenture, dated as of August 18, 2020, the Twenty-Fourth Supplemental Indenture, dated as of August 18, 2020, the Twenty-Fifth Supplemental Indenture, dated as of March 14, 2022, the Twenty-Sixth Supplemental Indenture, dated as of August 11, 2022, the Twenty-Seventh Supplemental Indenture, dated as of February 9, 2023 and the Twenty-Eighth Supplemental Indenture, dated as of February 9, 2023 (as so supplemented and together with the Base Indenture, the “Indenture”), in each case between the Partnership and the Trustee, the Partnership may from time to time issue and sell Debt Securities in one or more series;

WHEREAS, the Partnership desires to create and authorize a new series of Debt Securities entitled “5.500% Senior Notes due 2034” (the “Notes”), limited initially to $1,650,000,000 in aggregate principal amount, and to provide the terms and conditions upon which the Notes are to be executed, registered, authenticated, issued and delivered, the Partnership has duly authorized the execution and delivery of this Supplemental Indenture;

WHEREAS, the Notes are a series of Debt Securities and are being issued under the Indenture, as supplemented by this Supplemental Indenture, and are subject to the terms contained therein and herein;

WHEREAS, the Notes are to be substantially in the form attached hereto as Exhibit A; and

WHEREAS, all acts and things necessary to make the Notes, when executed by the Partnership and authenticated and delivered by or on behalf of the Trustee as provided in the Indenture and this Supplemental Indenture, the valid, binding and legal obligations of the Partnership, and to make this Supplemental Indenture a legal, binding and enforceable agreement, have been done and performed.

NOW, THEREFORE, in order to declare the terms and conditions upon which the Notes are executed, registered, authenticated, issued and delivered, and in consideration of the foregoing premises and the purchase of such Notes by the Holders thereof, the Partnership and the Trustee mutually covenant and agree, for the equal and proportionate benefit of the Holders from time to time of the Notes, as follows:

Section 1. Definitions. Terms used in this Supplemental Indenture and not defined herein shall have the respective meanings given such terms in the Indenture.

Section 2. Other Definitions. In addition, the following terms shall have the following meanings with respect to the Notes:

“Board Resolution” means a copy of a resolution or resolutions of the Board of Directors or an authorized committee or subcommittee thereof, certified by the Secretary or an Assistant Secretary of the General Partner to be in full force and effect on the date of such certification, and delivered to the Trustee.

“Consolidated Net Tangible Assets” means the aggregate value of all assets of the Partnership and its Subsidiaries after deducting therefrom: (i) all current liabilities, excluding all short-term indebtedness and the current portion of long-term indebtedness; (ii) all investments in unconsolidated subsidiaries and all investments accounted for on the equity basis; and (iii) all goodwill, patents and trademarks, unamortized debt discounts and other similar intangibles (all determined in conformity with generally accepted accounting principles and calculated on a basis consistent with the Partnership’s most recent audited consolidated financial statements).

“Interest Payment Date,” when used with respect to any installment of interest on any Debt Security, means the date specified in such Debt Security as the fixed date on which such installment of interest is due and payable.

“Mortgage” means as the context may require, (i) to mortgage, pledge, encumber or subject to a lien or (ii) a mortgage, pledge, encumbrance or lien.

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“Predecessor Security” of any particular Debt Security means every previous Debt Security evidencing all or a portion of the same debt as that evidenced by such particular Debt Security; and, for the purposes of this definition, any Debt Security authenticated and delivered under Section 2.09 of the Indenture in exchange for or in lieu of a mutilated, destroyed, lost or stolen Debt Security shall be deemed to evidence the same debt as the mutilated, destroyed, lost or stolen Debt Security.

“Regular Record Date” for the interest payable on any Interest Payment Date on the Debt Securities means the date specified for that purpose as contemplated by Section 2.03 of the Indenture.

“Special Record Date” for the payment of any Defaulted Interest means a date fixed by the Trustee pursuant to Section 2.17 of the Indenture.

Section 3. Creation and Authorization of Series.

(a) There is hereby created and authorized the following new series of Debt Securities to be issued under the Indenture, to be designated as the “5.500% Senior Notes due 2034.”

(b) The Notes shall be limited initially to $1,650,000,000 in aggregate principal amount. Notwithstanding the foregoing initial aggregate principal amount, the Partnership may, from time to time, without notice to or consent of the Holders of the Notes, increase the principal amount of the Notes that may be issued under this Supplemental Indenture and issue such increased principal amount (or any portion thereof), in which case any additional Notes so issued will have the same terms and conditions other than the public offering price, original interest accrual date and initial interest payment date, and the same CUSIP numbers as the applicable series of Notes previously issued, will be fungible with the applicable series of Notes previously issued for U.S. federal income tax purposes, and will carry the same right to receive accrued and unpaid interest as the Notes previously issued, and such additional notes will form a single series with the Notes of such series previously issued, including, without limitation, for purposes of waivers, amendments, redemptions and, if any, offers to purchase, and will rank equally and ratably with the Notes of such series previously issued.

(c) The date on which the principal is payable on the Notes, unless accelerated pursuant to the Indenture, shall be as provided in the form of security attached hereto as Exhibit A.

(d) The Notes shall bear interest as provided in the form of security attached hereto as Exhibit A. The Interest Payment Dates and the Regular Record Dates for the determination of Holders of the Notes to whom such interest is payable shall be as provided in the form of security attached hereto as Exhibit A.

(e) The Notes shall be redeemable at the option of the Partnership as set forth in the form of security attached hereto as Exhibit A.

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(f) For purposes of this Note only, Section 3.02 of the Base Indenture (Notice of Redemption; Selection of Debt Securities) is hereby amended to replace the number 30 with the number 10 in the first sentence of Section 3.02 of the Base Indenture.

(g) The provisions of Sections 3.04 and 3.05 of the Indenture shall not be applicable to the Notes.

(h) The Notes will be issued only in fully registered form, without coupons, in denominations provided herein and in the form of security attached hereto as Exhibit A.

(i) The Events of Default and covenants specified in the Indenture will apply to the Notes.

(j) For purposes of the provisions set forth in Sections 10.01 and 10.02 of the Indenture, “substantially all of the assets” shall mean, at any date, a portion of the non-current assets reflected in the Partnership’s consolidated balance sheet as of the end of the most recent quarterly period that represents at least sixty-six and two-thirds percent (66 2/3%) of the total reported value of such assets.

(k) The defeasance and covenant defeasance provisions of Article XI of the Indenture, including both Sections 11.02 and 11.03 of the Indenture, will apply to the Notes.

(l) The Notes shall be issued in the form of one or more Global Debt Securities substantially in the form of security attached hereto as Exhibit A. The Partnership initially appoints The Depository Trust Company to act as Depositary with respect to the Notes. Additional provisions applicable to the Notes issued in the form of a Global Security are set forth in the form of security attached hereto as Exhibit A.

(m) The Notes shall be issuable only in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

(n) The Trustee will initially act as the Registrar for the Notes and as the paying agent with respect to the Notes. The Place of Payment will be The Bank of New York Mellon Trust Company, N.A., c/o The Bank of New York Mellon, 240 Greenwich Street, New York, New York 10286.

(o) Except as otherwise set forth herein and in the Notes, the terms of the Notes shall be as set forth in the Indenture, including those made part of the Indenture by reference to the TIA.

Section 4. Additional Covenants. In addition to the covenants set forth in Article IV of the Indenture, the following additional covenants shall apply with respect to the Notes:

Section 4.10 Mortgage of Certain Property.

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If the Partnership or any Subsidiary of the Partnership shall Mortgage as security for any indebtedness for money borrowed any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, the Partnership will secure, or will cause such Subsidiary to secure, the Notes and all other Debt Securities equally and ratably with all indebtedness or obligations secured by the Mortgage then being given; provided, however, that this covenant shall not apply in the case of:

5

Notwithstanding the foregoing restriction contained in this Section 4.10, the Partnership may, and may permit its Subsidiaries to, incur liens or grant Mortgages on property covered by the restriction above so long as the net book value of the property so encumbered, together with all property subject to the restriction on sale and leasebacks contained in Section 4.11, does not, at the time such lien or Mortgage is granted, exceed fifteen percent (15%) of Consolidated Net Tangible Assets.

Section 4.11 Sale and Leaseback of Certain Properties.

The Partnership will not, nor will it permit any Subsidiary of the Partnership to, sell or transfer any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, with the intention of taking back a lease of such property; provided, however, this covenant shall not apply if:

6

In the event of such a sale or transfer, the Partnership shall deliver to the Trustee the Board Resolution referred to in the parenthetical phrase contained in subclause (4)(B) of this Section 4.11 and an Officer’s Certificate setting forth all material facts under this Section 4.11. For the purposes of this Section 4.11, the term “retirement” of such funded debt shall include the “in substance defeasance” of such funded debt in accordance with then applicable accounting rules.

Section 5. Effect of Supplemental Indenture. The provisions of this Supplemental Indenture are intended to supplement those of the Indenture as in effect immediately prior to the execution and delivery hereof. The Indenture shall remain in full force and effect except to the extent that the provisions of the Indenture are expressly modified by the terms of this Supplemental Indenture.

Section 6. Governing Law. This Supplemental Indenture and the Notes shall be governed by and construed in accordance with the law of the State of New York, without giving effect to any principles of conflicts of laws thereunder to the extent the application of the laws of another jurisdiction would be required thereby.

Section 7. Trustee Not Responsible for Recitals or Issuance of Notes. The recitals and statements contained herein shall be taken as statements of the Partnership, and the Trustee assumes no responsibility for their correctness. The Trustee makes no representations as to the validity or sufficiency of this Supplemental Indenture or of the Notes other than with respect to the Trustee’s authentication. The Trustee shall not be accountable for the use or application by the Partnership of the Notes or the proceeds thereof.

7

Section 8. Conflict with TIA. If any provision hereof limits, qualifies or conflicts with a provision of the TIA that is required under the TIA to be a part of and govern this Supplemental Indenture, the latter provision shall control. If any provision of this Supplemental Indenture modifies or excludes any provision of the TIA that may be so modified or excluded, the latter provision shall be deemed to apply to this Supplemental Indenture as so modified or to be excluded, as the case may be.

Section 9. Counterparts; Electronic Signature. This Supplemental Indenture may be executed in any number of counterparts, each of which shall be an original; but such counterparts shall together constitute one and the same instrument. The exchange of copies of this Supplemental Indenture and of signature pages that are executed by manual signatures that are scanned, photocopied or faxed or by other electronic signing created on an electronic platform (such as DocuSign) or by digital signing (such as Adobe Sign), in each case that is approved by the Trustee, shall constitute effective execution and delivery of this Supplemental Indenture for all purposes. Signatures of the parties hereto that are executed by manual signatures that are scanned, photocopied or faxed or by other electronic signing created on an electronic platform (such as DocuSign) or by digital signing (such as Adobe Sign), in each case that is approved by the Trustee, shall be deemed to be their original signatures for all purposes of the Supplemental Indenture as to the parties hereto and may be used in lieu of the original.

Anything in the Indenture, this Supplemental Indenture or the Notes to the contrary notwithstanding, for the purposes of the transactions contemplated by the Indenture, this Supplemental Indenture, the Notes and any document to be signed in connection with the Indenture, this Supplemental Indenture or the Notes (including amendments, waivers, consents and other modifications, Officer’s Certificates, Company Orders and Opinions of Counsel and other issuance, authentication and delivery documents) or the transactions contemplated hereby may be signed by manual signatures that are scanned, photocopied or faxed or other electronic signatures created on an electronic platform (such as DocuSign) or by digital signature (such as Adobe Sign), in each case that is approved by the Trustee, and contract formations on electronic platforms approved by the Trustee, and the keeping of records in electronic form, are hereby authorized, and each shall be of the same legal effect, validity or enforceability as a manually executed signature in ink or the use of a paper-based recordkeeping system, as the case may be.

Section 10. Sanctions. The Partnership covenants and represents to the Trustee that neither the Partnership nor any of the Partnership’s subsidiaries, or to the Partnership’s knowledge, any director, officer, employee, agent, affiliate or representative of the Partnership or any of the Partnership’s subsidiaries, is an individual or entity (“Person”) that is, or is owned or controlled by a Person that is:

8

(b) The Partnership will not, directly or indirectly, use any payments made pursuant to this Supplemental Indenture, or lend, contribute or otherwise make available such payments to any subsidiary, joint venture partner or other Person:

[The remainder of this page is left blank intentionally]

9

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the day and year first above written.

[Signature Page to Twenty-Ninth Supplemental Indenture]

[Signature Page to Twenty-Ninth Supplemental Indenture]

Exhibit A

MPLX LP

5.500% Senior Notes due 2034

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.

MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (herein called the “Partnership,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to CEDE & CO., or registered assigns, the principal sum of [•] ($[•]), or such greater or lesser amount as indicated on the Schedule of Increases or Decreases in the Principal Amount of Securities attached hereto, on June 1, 2034, and to pay interest thereon from May 20, 2024 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually on June 1 and December 1 in each year commencing December 1, 2024, at the rate of 5.500% per annum, until the principal hereof is paid or made available for payment. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be May 15 or November 15 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the

Holder on such Regular Record Date and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Debt Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Debt Securities of this series may be listed, and upon such notice as may be required by such exchange all as more fully provided in said Indenture. If an Interest Payment Date, a Stated Maturity or a Redemption Date with respect to this Security falls on a day that is not a Business Day, the payment will be made on the next Business Day and no interest will accrue for the period from and after such Interest Payment Date, Stated Maturity or Redemption Date.

Payment of the principal of (and premium, if any) and interest on this Security will be made at the office or agency of the Partnership maintained for that purpose in New York, New York, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, that (1) payments on any Global Security shall be made by electronic (same-day) funds transfer to the Depositary and (2) at the option of the Partnership, payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Debt Security Register or by electronic funds transfer to an account maintained by the Person entitled thereto as specified in the Debt Security Register, provided that such Person shall have given the Trustee written instructions.

Reference is hereby made to the further provisions of this Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, or, for purposes of this Debt Security only, by Adobe Sign or DocuSign, or such other digital signature or electronic platform or method as specified in writing by email to the Partnership (or to its counsel) by the Trustee (or its counsel), this Debt Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, the Partnership has caused this instrument to be duly executed.

Dated:

CERTIFICATE OF AUTHENTICATION

This is one of the Debt Securities of the series designated therein referred to in the within-mentioned Indenture.

Dated:

MPLX LP

5.500% Senior Notes due 2034

This Security is one of a duly authorized issue of Debt Securities of the Partnership (herein called the “Securities”), issued and to be issued in one or more series under a Senior Indenture, dated as of February 12, 2015, as amended or supplemented to date, including as supplemented and amended by the Twenty-Ninth Supplemental Indenture, dated as of May 20, 2024 (herein called the “Indenture,” which term shall have the meaning assigned to it in such instrument), between the Partnership and The Bank of New York Mellon Trust Company, N.A., as Trustee (herein called the “Trustee,” which term includes any successor trustee under the Indenture), and reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Partnership, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one of the series designated on the face hereof initially limited in aggregate principal amount to $1,650,000,000.

Prior to March 1, 2034, the Partnership may redeem the Securities at its option, in whole at any time or in part from time to time, at a redemption price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of (1) the sum of the present values of the remaining scheduled payments of principal and interest on the Securities to be redeemed discounted to the Redemption Date (assuming such Securities matured on March 1, 2034) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 20 basis points less interest accrued to the Redemption Date, and (2) 100% of the principal amount of such Securities to be redeemed, plus, in either case, accrued and unpaid interest thereon to the Redemption Date.

On or after March 1, 2034, the Partnership may redeem the Securities in whole at any time or in part from time to time, at a redemption price equal to 100% of the principal amount of such Securities to be redeemed plus accrued and unpaid interest thereon to the Redemption Date.

For purposes of the redemption provisions of the Securities, the following terms are applicable:

“Business Day” means any Monday, Tuesday, Wednesday, Thursday or Friday that is not a day on which banking institutions in New York, New York or any Place of Payment are authorized or obligated by law, regulation or executive order to close.

“Treasury Rate” means, with respect to any Redemption Date, the yield determined by the Partnership in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Partnership after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third

Business Day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Partnership shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to March 1, 2034 (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to March 1, 2034 on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

If on the third Business Day preceding the Redemption Date, the Treasury constant maturity described above is no longer displayed on H.15, or if H.15 is no longer published, the Partnership shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second Business Day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, March 1, 2034. If there is no United States Treasury security maturing on March 1, 2034 but there are two or more United States Treasury securities with a maturity date equally distant from March 1, 2034, one with a maturity date preceding March 1, 2034 and one with a maturity date following March 1, 2034, the Partnership shall select the United States Treasury security with a maturity date preceding March 1, 2034. If there are two or more United States Treasury securities maturing on March 1, 2034 or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Partnership shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time, of such United States Treasury security, and rounded to three decimal places.

The Partnership’s actions and determinations in determining the redemption price shall be conclusive and binding for all purposes, absent manifest error. The Partnership will notify the Trustee of the redemption price promptly after the calculation thereof and the Trustee shall not be responsible or liable for any calculation of

the redemption price or of any component thereof, or for determining whether manifest error has occurred.

Unless the Partnership defaults in payment of the redemption price, on or after the Redemption Date, interest will cease to accrue on the Securities or portions thereof called for redemption.

In the case of a partial redemption, selection of the Securities for redemption will be made pro rata, by lot or by such other method as the Trustee in its sole discretion deems appropriate and fair. No Securities of a principal amount of $2,000 or less will be redeemed in part. If any Security is to be redeemed in part only, the notice of redemption that relates to the Security will state the portion of the principal amount of the Security to be redeemed.

The Indenture contains provisions for defeasance at any time of the entire indebtedness of this Security or of certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth in the Indenture.

The Indenture contains provisions permitting the Partnership and the Trustee to modify the Indenture or any supplemental indenture without the consent of the Holders for one or more of the following purposes: (1) to evidence the succession of another Person to the Partnership; (2) to surrender any right or power conferred by the Indenture, to add to the covenants for the protection of the Holders of the Securities or to add additional defaults or events of default; (3) to cure any ambiguity, to correct or supplement any provision of the Indenture which may be defective or inconsistent with any other provision of the Indenture, or to make any other provisions with respect to matters or questions arising under the Indenture as shall not adversely affect the interests of the Holders; (4) to permit qualification of the Indenture or any supplemental indenture under the TIA; (5) to permit or facilitate the issuance of Debt Securities of any series in uncertificated form; (6) to secure any or all Debt Securities; (7) to make any change that does not adversely affect the rights of any Holder; (8) to add to, change or eliminate any of the provisions of the Indenture in respect of one or more Debt Securities, under certain conditions specified therein; (9) to evidence and provide acceptance of appointment thereunder by a successor or separate Trustee and to add to or change the provisions under the Indenture as necessary; and (10) to establish the form or terms of Debt Securities of any series as permitted by Sections 2.01 and 2.03 of the Indenture.

The Indenture also permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Partnership and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Partnership and the Trustee with the consent of the Holders of not less than a majority in aggregate principal amount of the Securities at the time Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of at least a majority in aggregate principal amount of the Securities at the time Outstanding, on behalf of the Holders of all Securities, to waive compliance by the Partnership with certain provisions of the Indenture and certain past

defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

As provided in and subject to the provisions of the Indenture, the Holder of this Security shall not have the right to institute any proceeding with respect to the Indenture or for the appointment of a receiver or trustee or for any other remedy thereunder, unless such Holder shall have previously given the Trustee written notice of a continuing Event of Default with respect to the Securities, the Holders of not less than 25% in aggregate principal amount of the Securities then Outstanding shall have made written request to the Trustee to institute proceedings in respect of such Event of Default as Trustee and offered the Trustee indemnity, and the Trustee shall not have received from the Holders of a majority in principal amount of the Securities then Outstanding a direction inconsistent with such request, and shall have failed to institute any such proceeding, for 60 days after receipt of such notice, request and offer of indemnity. The foregoing shall not apply to any suit instituted by the Holder of this Security for the enforcement of any payment of principal hereof or any premium or interest hereon on or after the respective due dates expressed herein.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Partnership, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registrable in the Debt Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Partnership in any place where the principal of and any premium and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Partnership and the Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities are issuable only in registered form without coupons in denominations of $2,000 and integral multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, the Securities are exchangeable for a like aggregate principal amount of Securities and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but, subject to any applicable provisions of the Indenture, the Partnership may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Partnership, the Trustee and any agent of the Partnership or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Partnership, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meaning assigned to them in the Indenture.

FORM OF ASSIGNMENT

ABBREVIATIONS

Customary abbreviations may be used in the name of a Securityholder or an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the entireties), JT TEN (=joint tenants with rights of survivorship and not as tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors Act).

Additional abbreviations may also be used though not in the above list.

FOR VALUE RECEIVED, the undersigned hereby sell(s),

assign(s) and transfer(s) unto

Please insert Social Security or

other identifying number of assignee

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE

the within Security and all rights thereunder, hereby irrevocably constituting and appointing _____________________ attorney to transfer said Security on the books of the Partnership, with full power of substitution in the premises.

SCHEDULE OF INCREASES OR DECREASES IN THE PRINCIPAL AMOUNT OF SECURITIES

The original principal amount of this Security is [•] U.S. Dollars ($[•]). The following increases or decreases in the principal amount of this Security have been made:

Exhibit 5.1

NORTH POINT • 901 LAKESIDE AVENUE • CLEVELAND, OHIO 44114.1190

TELEPHONE: +1.216.586.3939 • JONESDAY.COM

May 20, 2024

MPLX LP

200 E. Hardin Street

Findlay, Ohio 45840

Ladies and Gentlemen:

We are acting as counsel for MPLX LP, a Delaware limited partnership (the “Partnership”), in connection with the issuance and sale of $1,650,000,000 aggregate principal amount of the Partnership’s 5.500% Senior Notes due 2034 (the “Notes”), pursuant to the Underwriting Agreement, dated May 15, 2024, among the Partnership, MPLX GP LLC, a Delaware limited liability company and the general partner of the Partnership (the “General Partner”), and Mizuho Securities USA LLC, RBC Capital Markets, LLC and TD Securities (USA) LLC, acting as representatives of the several underwriters named therein. The Notes will be issued pursuant to a senior indenture, dated as of February 12, 2015 (as amended, supplemented or otherwise modified to the date hereof, the “Base Indenture”), between the Partnership and The Bank of New York Mellon Trust Company, N.A., as trustee (the “Trustee”), as supplemented by the Twenty-Ninth Supplemental Indenture, dated as of the date hereof (together with the Base Indenture, the “Indenture”), between the Partnership and the Trustee.

In connection with the opinion expressed herein, we have examined such documents, records and matters of law as we have deemed relevant or necessary for purposes of such opinion. Based on the foregoing, and subject to the further limitations, qualifications and assumptions set forth herein, we are of the opinion that the Notes constitute valid and binding obligations of the Partnership.

For the purposes of the opinion expressed herein, we have assumed that (i) the Trustee has authorized, executed and delivered the Indenture, (ii) the Notes have been duly authenticated by the Trustee in accordance with the terms of the Indenture and (iii) the Indenture is the valid, binding and enforceable obligation of the Trustee.

The opinion expressed herein is limited by (i) bankruptcy, insolvency, reorganization, fraudulent transfer and fraudulent conveyance, voidable preference, moratorium or other similar laws and related regulations and judicial doctrines from time to time in effect relating to or

AMSTERDAM • ATLANTA • BEIJING • BOSTON • BRISBANE • BRUSSELS • CHICAGO • CLEVELAND • COLUMBUS • DALLAS

DETROIT • DUBAI • DÜSSELDORF • FRANKFURT • HONG KONG • HOUSTON • IRVINE • LONDON • LOS ANGELES • MADRID

MELBOURNE • MEXICO CITY • MIAMI • MILAN • MINNEAPOLIS • MUNICH • NEW YORK • PARIS • PERTH • PITTSBURGH

SAN DIEGO • SAN FRANCISCO • SÃO PAULO • SHANGHAI • SILICON VALLEY • SINGAPORE • SYDNEY • TAIPEI • TOKYO • WASHINGTON

MPLX LP

May 20, 2024

Page 2

affecting creditors’ rights generally and (ii) general equitable principles and public policy considerations, whether such principles and considerations are considered in a proceeding at law or at equity.

As to facts material to the opinion and assumptions expressed herein, we have relied upon oral or written statements and representations of the officers and other representatives of the General Partner and others.

The opinion expressed herein is limited to the Delaware Revised Uniform Limited Partnership Act and the laws of the State of New York, in each case as currently in effect, and we express no opinion as to the effect of the laws of any other jurisdiction.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Current Report on Form 8-K dated the date hereof filed by the Partnership and incorporated by reference into the Registration Statement on Form S-3 (Registration No. 333-271922) (the “Registration Statement”), filed by the Partnership to effect the registration of the Notes under the Securities Act of 1933 (the “Act”) and to the reference to Jones Day under the caption “Legal Matters” in the prospectus constituting a part of such Registration Statement. In giving such consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Securities and Exchange Commission promulgated thereunder.