CRZO Carrizo Oil and Gas Inc

Filed by: Carrizo Oil & Gas, Inc.

(Commission File No.: 000-29187-87)

Pursuant to Rule 425 under the Securities Act of 1933

and deemed filed pursuant to 14a-6

of the Securities Exchange Act of 1934

Subject Company: Carrizo Oil & Gas, Inc.

Form S-4 File No.: 333-233366

On October 14, 2019, the President and Chief Executive Officer of Callon Petroleum Company (“Callon”) and the President and Chief Executive Officer of Carrizo Oil & Gas, Inc. (“Carrizo”) distributed the following communication to employees of Callon and Carrizo:

Dear Callon and Carrizo employees,

We are pleased to share that progress continues towards closing of the merger to combine our companies. Last week, we filed the definitive proxy statement which allows us to begin soliciting votes from Callon and Carrizo shareholders. The special meetings for both companies’ shareholders will be held on Thursday, November 14, 2019, at 9:00 a.m. at separate locations in Houston. Assuming the shareholders approve the merger agreement, we would expect to proceed to closing within a week.

We invite all of you who own shares in Callon and Carrizo stock vote in favor of all of the shareholder proposals. The proxy statement includes specific information on how to vote. For those of you with CPE or CRZO shares in your Fidelity brokerage account, detailed voting instructions will be available later this week here. If you own shares in your 401(k) plan account, voting instructions will be mailed to you according to the communication settings you have established for that account.

In the meantime, progress continues on all fronts for our integration efforts. We are all very encouraged to see the Callon and Carrizo teams working together so closely to make this combination a success. While we advance our integration plans and proceed to closing, please stay focused on continuing to safely and responsibly deliver on our 2019 commitments. We appreciate your support throughout this process and will continue to provide updates as they become available.

Joe & Chip

No Offer or Solicitation

Communications herein do not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval with respect to the proposed transaction or otherwise, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. Communication herein do not constitute a notice of redemption with respect to or an offer to purchase or sell (or the solicitation of an offer to purchase or sell) any preferred stock of Carrizo Oil & Gas, Inc.

Additional Information and Where to Find It

In connection with the proposed transaction, Callon Petroleum Company (“Callon”) has filed, and the Securities and Exchange Commission (the “SEC”) has declared effective, a registration statement on Form S-4 (the “Registration Statement”), which contains a joint proxy statement of Callon and Carrizo that also constitutes a prospectus of Callon. This communication is not a substitute for the joint proxy statement/prospectus or the Registration Statement or for any other document that Callon or

Carrizo may file with the SEC and/or send to Callon’s shareholders and/or Carrizo’s shareholders in connection with the proposed transaction. INVESTORS AND SECURITY HOLDERS OF CALLON AND CARRIZO ARE URGED TO READ THE REGISTRATION STATEMENT AND JOINT PROXY STATEMENT/PROSPECTUS, AS EACH MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, AND OTHER RELEVANT DOCUMENTS FILED BY CALLON AND CARRIZO WITH THE SEC CAREFULLY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT CALLON, CARRIZO AND THE PROPOSED TRANSACTION.

Investors will be able to obtain free copies of the Registration Statement and joint proxy statement/prospectus, as each may be amended from time to time, and other relevant documents filed by Callon and Carrizo with the SEC (when they become available) through the website maintained by the SEC at www.sec.gov. Copies of documents filed with the SEC by Callon will be available free of charge from Callon’s website at www.callon.com under the “Investors” tab or by contacting Callon’s Investor Relations Department at (281) 589-5200 or IR@callon.com. Copies of documents filed with the SEC by Carrizo will be available free of charge from Carrizo’s website at www.carrizo.com under the “Investor Relations” tab or by contacting Carrizo’s Investor Relations Department at (713) 328-1055 or IR@carrizo.com.

Participants in the Proxy Solicitation

Callon, Carrizo and their respective directors and certain of their executive officers and other members of management and employees may be deemed, under SEC rules, to be participants in the solicitation of proxies from Callon’s shareholders and Carrizo’s shareholders in connection with the proposed transaction. Information regarding the executive officers and directors of Callon is included in its definitive proxy statement for its 2019 annual meeting filed with the SEC on March 27, 2019. Information regarding the executive officers and directors of Carrizo is included in its definitive proxy statement for its 2019 annual meeting filed with the SEC on April 2, 2019. Additional information regarding the persons who may be deemed participants and their direct and indirect interests, by security holdings or otherwise, will be set forth in the Registration Statement and joint proxy statement/prospectus and other materials when they are filed with the SEC in connection with the proposed transaction. Free copies of these documents may be obtained as described in the paragraphs above.

Cautionary Statement Regarding Forward-Looking Information

Certain statements in this communication concerning the proposed transaction, including any statements regarding the expected timetable for completing the proposed Carrizo transaction, the results, effects, benefits and synergies of the proposed transaction, future opportunities for the combined company, future financial performance and condition, guidance and any other statements regarding Callon’s or Carrizo’s future expectations, beliefs, plans, objectives, financial conditions, assumptions or future events or performance that are not historical facts are “forward-looking” statements based on assumptions currently believed to be valid. Forward-looking statements are all statements other than statements of historical facts. The words “anticipate,” “believe,” “ensure,” “expect,” “if,” “intend,” “estimate,” “probable,” “project,” “forecasts,” “predict,” “outlook,” “aim,” “will,” “could,” “should,” “would,” “potential,” “may,” “might,” “anticipate,” “likely” “plan,” “positioned,” “strategy,” and similar expressions or other words of similar meaning, and the negatives thereof, are intended to identify forward-looking statements. The forward-looking statements are intended to be subject to the safe harbor provided by Section 27A of the Securities Act of 1933, Section 21E of the Securities Exchange Act of 1934 and the Private Securities Litigation Reform Act of 1995.

These forward-looking statements involve significant risks and uncertainties that could cause actual results to differ materially from those anticipated, including, but not limited to, failure to obtain the required votes of Callon’s shareholders or Carrizo’s shareholders to approve the transaction and related matters; whether any redemption of Carrizo’s preferred stock will be necessary or will occur prior to the closing of the transaction; the risk that a condition to closing of the proposed transaction may not be satisfied, that either party may terminate the merger agreement or that the closing of the proposed transaction might be delayed or not occur at all; potential adverse reactions or changes to business or employee relationships, including those resulting from the announcement or completion of the transaction; the diversion of management time on transaction-related issues; the ultimate timing, outcome and results of integrating the operations of Callon and Carrizo; the effects of the business combination of Callon and Carrizo, including the combined company’s future financial condition, results of operations, strategy and plans; the ability of the combined company to realize anticipated synergies in the timeframe expected or at all; changes in capital markets and the ability of the combined company to finance operations in the manner expected; regulatory approval of the transaction; the effects of commodity prices; and the risks of oil and gas activities. Expectations regarding business outlook, including changes in revenue, pricing, capital expenditures, cash flow generation, strategies for our operations, oil and natural gas market conditions, legal, economic and regulatory conditions, and environmental matters are only forecasts regarding these matters.

Additional factors that could cause results to differ materially from those described above can be found in Callon’s Annual Report on Form 10-K for the year ended December 31, 2018 and in its subsequent Quarterly Reports on Form 10-Q for the quarter ended March 31, 2019, and the quarter ended June 30, 2019, each of which is on file with the SEC and available from

Callon’s website at www.callon.com under the “Investors” tab, and in other documents Callon files with the SEC, and in Carrizo’s Annual Report on Form 10-K for the year ended December 31, 2018 and in its subsequent Quarterly Reports on Form 10-Q for the quarter ended March 31, 2019, and the quarter ended June 30, 2019, each of which is on file with the SEC and available from Carrizo’s website at www.carrizo.com under the “Investor Relations” tab, and in other documents Carrizo files with the SEC.

All forward-looking statements speak only as of the date they are made and are based on information available at that time. Neither Callon nor Carrizo assumes any obligation to update forward-looking statements to reflect circumstances or events that occur after the date the forward-looking statements were made or to reflect the occurrence of unanticipated events except as required by federal securities laws. As forward-looking statements involve significant risks and uncertainties, caution should be exercised against placing undue reliance on such statements.