Pioneer Natural Resources Co. and Pioneer Southwest Energy Partners L.P. jointly announced the completion of the merger of Pioneer Southwest with a wholly-owned subsidiary of Pioneer, with Pioneer Southwest surviving the merger as an indirect wholly-owned subsidiary of Pioneer, effective December 17. Under the merger agreement, each Pioneer Southwest unitholder eligible to receive the merger consideration will receive 0.2325 of a share of Pioneer common stock for each Pioneer Southwest common unit owned by such unitholder, plus, after aggregating all fractions of shares to which such unitholder would be entitled, a whole share of Pioneer common stock in lieu of any fractional share of Pioneer common stock otherwise issuable to such unitholder in the merger. As a result of the completion of the merger, common units of Pioneer Southwest will cease trading at the close of business today. Shares of Pioneer common stock will continue to be traded on the New York Stock Exchange under the ticker symbol “PXD.”

The consolidation of the properties of Pioneer and Pioneer Southwest in the Midland basin in West Texas pursuant to the merger is expected to facilitate Pioneer’s plans to fully and optimally develop the area utilizing horizontal drilling and is expected to provide organizational, operational and administrative efficiencies.