2009-06-12 17:49:01 -

Pioneer Southwest Energy Partners L.P. (“Pioneer Southwest”) (NYSE:PSE) today announced its second quarter 2009 earnings press release is scheduled to be issued after the close of trading on the New York Stock Exchange on Tuesday, August 4, 2009.

A conference call is scheduled for Wednesday, August 5, 2009 at 11:00 a.m. CT to discuss the second quarter results. Instructions on how

to listen to the call and view the accompanying presentation are shown below.

Internet: www.pioneersouthwest.com :

Select “Investors,” then “Earnings Calls & Webcasts” to listen to the discussion and view the presentation.

Telephone: Dial (877) 723-9517, confirmation code: 4416045 five minutes before the call to listen to the discussion. View the presentation via Pioneer Southwest’s internet address above.

A replay of the webcast will be archived on Pioneer Southwest’s website.

A telephone replay will be available through August 28 by dialing (888) 203-1112, confirmation code: 4416045.

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 Wednesday, August 5, 2009 at 9:00 a.m. CT, Pioneer Natural Resources Company (“PNRC”) will conduct its second quarter 2009 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) 874-1565, confirmation code: 8449625, five minutes before the call. The accompanying presentation can be viewed at 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 28 by dialing (888) 203-1112, confirmation code: 8449625.

Pioneer Southwest Energy Partners L.P.InvestorsFrank

Hopkins, 972-969-4065Nolan Badders, 972-969-3955orMedia
and Public AffairsSusan Spratlen, 972-969-4018