Pioneer Southwest Proposes Initial Public Offering

Pioneer Southwest Energy Partners filed a registration statement on Form S-1 with the Securities and Exchange Commission related to the proposed initial public offering of Pioneer Southwest Energy common units.

Pioneer Southwest Energy anticipates offering 12,500,000 common units in the initial public offering representing a 44.4% limited partner interest in Pioneer Southwest Energy. Upon completion of this offering, Pioneer will own a 0.1% general partner interest and a 55.5% limited partner interest in Pioneer Southwest Energy. The underwriters are expected to be granted a 30-day option to purchase up to 1,875,000 additional common units. Pioneer's limited partner interest would be reduced to 52.0% if the underwriters exercise their over-allotment option in full. Pioneer Southwest Energy intends to apply to have its common units listed on the New York Stock Exchange under the ticker "PSE."

Assuming an initial public offering price of $20.00 per common unit and that the underwriters do not exercise their over-allotment option, estimated gross proceeds from the offering would be $250 million.

Pioneer Southwest Energy is a Delaware limited partnership formed by Pioneer to own producing oil and gas properties in the Spraberry field in the Permian Basin of West Texas, and to acquire producing oil and gas properties in its area of operations. This area includes onshore Texas (excluding 20 counties in the Texas Panhandle) and eight counties in the southeast region of New Mexico. Pioneer Southwest Energy will have interests in producing wells that had estimated proved reserves of 25.0 million barrels oil equivalent as of December 31, 2006 and average production of 4,611 barrels oil equivalent per day during 2006.