PSE Pioneer Southwest Energy Partners L.P. Pioneer Southwest Energy Partners Lp

Pioneer Southwest Energy Partners L.P. (�Pioneer Southwest�) (NYSE:PSE) announces its second quarter 2008 earnings conference call and webcast will be on Tuesday, August 5, 2008 at 11:30 a.m. CT. Instructions on how to listen to the call or the webcast and view the accompanying presentation are shown below. Telephone: Dial (877) 795-3610, confirmation code: 1064543 five minutes before the call to listen to the discussion. View the presentation via Pioneer Southwest�s internet address below. Internet: http://www.pioneersouthwest.com Select �Investors�, then �Earnings Calls & Webcasts� to listen to the discussion and view the presentation. A replay of the webcast will be archived on Pioneer Southwest�s website. A telephone replay will be available through August 29 by dialing (888) 203-1112, confirmation code: 1064543. Pioneer Southwest is a Delaware limited partnership formed by Pioneer Natural Resources Company to own and acquire oil and gas assets in its area of operations. This area includes onshore Texas and eight counties in the southeast region of New Mexico. Special Notice Regarding Pioneer Natural Resources Company Second Quarter Earnings Call. On Tuesday, August 5, 2008 at 10:00 a.m. CT, Pioneer Natural Resources Company (�PNRC�) will conduct its second quarter 2008 earnings conference call and webcast. Pioneer Southwest was formed by PNRC to own and acquire oil and gas assets in Pioneer Southwest�s area of operations. As such, it is possible that discussion on the PNRC call will include matters regarding Pioneer Southwest. To listen to the PNRC call dial (877) 741-4245, confirmation code: 1498320, five minutes before the call. The accompanying presentation can be viewed at http://www.pxd.com. Select �Investors�, then �Earnings Calls & Webcasts� to listen to the discussion and view the presentation. A replay of the webcast will be archived on PNRC�s website. A telephone replay will be available through August 29 by dialing (888) 203-1112, confirmation code: 1498320.