Pioneer Natural Resources Company Makes Proposal to Acquire the Publicly-Held Units of Pioneer Southwest Energy Partners L.P.

Pioneer Natural Resources Company (NYSE:PXD) ('Pioneer?) today
announced that it has submitted a proposal to the chairman of the
Conflicts Committee of the board of directors of the general partner of
Pioneer Southwest Energy Partners L.P. (NYSE:PSE) ('Pioneer Southwest?)
to purchase all of Pioneer Southwest′s outstanding publicly-held units
through a stock-for-unit exchange. Subject to negotiation and execution
of a definitive agreement, Pioneer is proposing consideration of 0.2234
of a share of Pioneer common stock for each outstanding publicly-held
Pioneer Southwest common unit. In proposing the 0.2234 exchange ratio,
Pioneer has assumed that a regular quarterly common unit distribution of
$0.52 per common unit will be declared in July and that, thereafter,
common unit distributions will be suspended while the transaction is
pending. The proposed transaction would be structured as a merger of
Pioneer Southwest with a wholly-owned subsidiary of Pioneer. The
proposal was referred to the Conflicts Committee of the general partner
of Pioneer Southwest, which will study, review and evaluate the
proposal. There can be no assurance that a definitive agreement will be
executed or that any transaction will be approved or consummated.

The consolidation of the properties of Pioneer and Pioneer Southwest in
the Midland Basin in West Texas through this proposed transaction would
facilitate Pioneer′s plans to fully and optimally develop the area and
would provide organizational, operational and administrative
efficiencies. Pioneer owns 100% of the general partner of Pioneer
Southwest and owns approximately 52.4% of the 35,713,700 outstanding
common units of Pioneer Southwest.

Pioneer is a large independent oil and gas exploration and production
company, headquartered in Dallas, Texas, with operations in the United
States.

This communication does not constitute an offer to sell any securities.
Any such offer will be made only by means of a prospectus, and only if
and when a definitive agreement has been entered into by Pioneer and
Pioneer Southwest, pursuant to a registration statement filed with the
Securities and Exchange Commission.

If Pioneer Southwest accepts Pioneer′s proposal and executes a
definitive agreement, a registration statement of Pioneer, which will
include a proxy statement and will constitute a prospectus of Pioneer,
and other materials will be filed with the Securities and Exchange
Commission. If and when applicable, investors and security holders are
urged to carefully read the documents filed with the Securities and
Exchange Commission regarding the proposed transaction when they become
available, because they will contain important information about
Pioneer, Pioneer Southwest and the proposed merger. If and when
applicable, investors and security holders may obtain a free copy of the
proxy statement / prospectus and other documents containing information
about Pioneer and Pioneer Southwest, without charge, at the Securities
and Exchange Commission′s website at www.sec.gov.

Pioneer, Pioneer Southwest and certain of their respective directors and
executive officers may be deemed to be participants in the solicitation
of proxies from the unitholders of Pioneer Southwest in connection with
the proposed transaction. Information about the directors and executive
officers of Pioneer is set forth in its proxy statement for its 2013
annual meeting of stockholders, which was filed with the Securities and
Exchange Commission on April ?11, 2013. Information about the directors
and executive officers of the general partner of Pioneer Southwest is
set forth in Pioneer Southwest′s Annual Report on Form 10-K for the year
ending December 31, 2012, which was filed with the Securities and
Exchange Commission on March 14, 2013. These documents can be obtained
without charge at the Securities and Exchange Commission′s website
indicated above. Additional information regarding the interests of these
participants may be obtained by reading the proxy statement / prospectus
regarding the proposed transaction when it becomes available.

Except for historical information contained herein, the statements
contained herein related to Pioneer's proposal to the Conflicts
Committee of the board of directors of the general partner of Pioneer
Southwest, and the transactions proposed therein, are forward-looking
statements that are made in reliance on the Safe Harbor Provisions of
the Private Securities Litigation Reform Act of 1995.Forward-looking
statements of Pioneer are subject to a number of risks and uncertainties
that may cause Pioneer's actual results in future periods to differ
materially from the forward-looking statements, including the risk that
the proposed transaction is not consummated at all or on the initial
terms proposed. These and other risks are described in Pioneer's annual,
quarterly and other reports filed with the Securities and Exchange
Commission.In addition, Pioneer may be subject to currently
unforeseen risks that may have a materially adverse effect on it.
Pioneer undertakes no duty to publicly update these statements except as
required by law.

Pioneer Natural Resources Company

Investors

Frank
Hopkins, 972-969-4065

or

Josh Jones, 972-969-5822

or

Media
and Public Affairs

Susan Spratlen, 972-969-4018

or

Suzanne
Hicks, 972-969-4020