SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): December 12, 2011

PIONEER SOUTHWEST ENERGY PARTNERS L.P.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (972) 444-9001

Not applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the Registrant under any of the following provisions:

PIONEER SOUTHWEST ENERGY PARTNERS L.P.

Pioneer Southwest Energy Partners L.P.’s (the “Partnership”) plans for 2012 include increasing to a three drilling rig program, which the Partnership expects to allow it to drill between 55 wells and 60 wells in 2012. The Partnership plans to drill substantially all of these wells to the Strawn formation, and approximately 35% of the wells to the deeper Atoka formation, to achieve incremental production. The Partnership’s capital budget for this program for 2012 is expected to range from $110 million to $120 million. Based on the planned 2012 drilling program, average daily production for 2012 is expected to increase by approximately 10% as compared to estimated 2011 production.

Cautionary Statement Concerning Forward-Looking Statements

The information in this Current Report on Form 8-K (the “Report”) contains forward-looking statements that involve risks and uncertainties. When used in this document, the words “believes,” “plans,” “expects,” “intends,” “may,” “will,” “could,” “should,” “future,” “estimate” or the negative of such terms and similar expressions as they relate to the Partnership are intended to identify forward-looking statements. The forward-looking statements are based on the Partnership’s current expectations, assumptions, estimates and projections about the Partnership and the industry in which the Partnership operates. Although the Partnership believes that the expectations and assumptions reflected in the forward-looking statements are reasonable, they involve risks and uncertainties that are difficult to predict and, in many cases, beyond the Partnership’s control.

These risks and uncertainties include, among other things, volatility of commodity prices, the effectiveness of the Partnership’s commodity price derivative strategy, reliance on Pioneer Natural Resources Company and its subsidiaries to manage the Partnership’s business and identify and evaluate drilling opportunities and acquisitions, product supply and demand, competition, the ability to obtain environmental and other permits and the timing thereof, other government regulation or action, the ability to obtain approvals from third parties and negotiate agreements with third parties on mutually acceptable terms, litigation, the costs and results of drilling and operations, availability of equipment, services and personnel required to complete the Partnership’s operating activities, access to and availability of transportation, processing and refining facilities, the Partnership’s ability to replace reserves, including through acquisitions, and implement its business plans or complete its development activities as scheduled, uncertainties associated with acquisitions, access to and cost of capital, the financial strength of counterparties to the Partnership’s credit facility and derivative contracts and the purchasers of the Partnership’s oil, NGL and gas production, uncertainties about estimates of reserves and the ability to add proved reserves in the future, the assumptions underlying production forecasts, quality of technical data and environmental and weather risks, including the possible impacts of climate change. These and other risks are described in the Partnership’s Annual Report on Form 10-K, its Quarterly Reports on Form 10-Q and other filings with the United States Securities and Exchange Commission. In addition, the Partnership may be subject to currently unforeseen risks that may have a materially adverse effect on it. Accordingly, no assurances can be given that the actual events and results will not be materially different than the anticipated results described in the forward-looking statements. See “Part I, Item 1. Business — Competition, Markets and Regulations,” “Part I, Item 1A. Risk Factors,” “Part II, Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations” and “Part II, Item 7A. Quantitative and Qualitative Disclosures About Market Risk” in the Partnership’s Annual Report on Form 10-K for the year ended December 31, 2010 and “Part II, Item 1A. Risk Factors” in the Partnership’s Quarterly Report on Form 10-Q for the quarters ended September 30, 2011, and June 30, 2011 for a description of various factors that could materially affect the ability of the Partnership to achieve the anticipated results described in the forward-looking statements. Readers are cautioned not to place undue reliance on forward-looking statements, which speak only as of the date hereof. The Partnership undertakes no duty to publicly update these statements except as required by law.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Dated: December 12, 2011