Pioneer Southwest Energy Partners L.P. Announces Fourth Quarter 2011 Earnings Press Release Date and Conference Call

Pioneer Southwest Energy Partners L.P. (“Pioneer Southwest”) (NYSE:PSE) today announced its fourth quarter 2011 earnings press release is scheduled to be issued after the close of trading on the New York Stock Exchange on Monday, February 6, 2012.

A conference call is scheduled for Tuesday, February 7, 2012 at 11:00 a.m. CT to discuss the fourth 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 [phone] confirmation code: 4119537 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 February 28 by dialing [phone], confirmation code: 4119537.

Pioneer Southwest is a Delaware limited partnership headquartered in Dallas, Texas, with current production and drilling operations in the Spraberry field in West Texas.

Special Notice Regarding Pioneer Natural Resources Company Fourth Quarter Earnings Call: On Tuesday, February 7 at 9:00 a.m. CT, Pioneer Natural Resources Company (“PNRC”) will conduct its fourth quarter 2011 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 [phone] confirmation code: 7754248 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 February 28 by dialing [phone], confirmation code: 7754248.