HOUSTON--(BUSINESS WIRE)--Feb. 23, 2012-- ATP Oil & Gas Corporation (NASDAQ:ATPG) today announced an increase in its estimated year-end 2011 proved and probable pre-tax PV-10 value to $7.3 billion based on SEC pricing, up 52% from $4.8 billion at year-end 2010. ATP also provided an update on production for full-year 2011 which averaged an estimated 24.6 thousand barrels per day (MBoe/d), an increase of 17% over 2010.

Reserves – ATP estimates year-end 2011 proved reserves of 118.9 MMBoe compared to 126.1 MMBoe at year-end 2010. ATP estimates proved and probable reserves of 194.4 MMBoe at year-end 2011, compared to 211.3 MMBoe at year-end 2010. The changes were primarily a result of production of 9.0 MMBoe in 2011 and revisions to oil and gas reserves. On a Boe basis, ATP estimates that oil and natural gas liquids (NGLs) represent 66% of its year-end 2011 proved reserves and 65% of proved and probable reserves, compared to 60% and 59%, respectively, at year-end 2010.

ATP estimates a year-end 2011 SEC pre-tax PV-10 value of $4.2 billion for its proved reserves and $7.3 billion for its proved and probable reserves, compared to $2.6 billion and $4.8 billion, respectively, at year-end 2010. This increase is primarily a result of pricing, but other factors include timing and an increase in oil and NGL reserves.

Since independent reservoir engineers are finalizing estimates of ATP's oil and natural gas reserves for year-end 2011, ATP will issue its final reserve amounts utilizing SEC pricing and reconciliation in conjunction with filing its Form 10-K, anticipated in March 2012.

Production - ATP's production in the fourth quarter 2011 averaged 24.8 MBoe/d compared to 24.2 MBoe/d in the third quarter 2011. The fourth quarter average benefited from a 1.4 MBoe/d recognition of royalty relief related to 2010 production. Not including this benefit, average production in the fourth quarter was 23.4 MBoe/d, of which 70% was oil, compared to 69% in the third quarter 2011. ATP intends to conduct the previously announced sleeve shift at the Mississippi Canyon (MC) 941 A-1 well in the first quarter 2012 after production is established at the MC 942 #2 well. This sleeve shift had previously been scheduled in the fourth quarter of 2011. ATP estimates that opening the sleeve in the MC 941 A-1 well will increase production by 1.5 MBoe/d.

ATP anticipates an increase in production from the completion of the MC 942 #2 well during the first quarter 2012 and an increase later in the year with the installation of the pipeline for the two Clipper wells that were completed and tested in 2011. The installation of the Clipper pipeline is scheduled to begin in the third quarter 2012 with production expected in the late third quarter/early fourth quarter 2012.

About ATP Oil & Gas Corporation

ATP Oil & Gas is an international offshore oil and gas development and production company with operations in the Gulf of Mexico, Mediterranean Sea and the North Sea. The company trades publicly as ATPG on the NASDAQ Global Select Market. For more information about ATP Oil & Gas Corporation, visit www.atpog.com.

Forward-looking Statements

Certain statements included in this news release contain "forward-looking statements" within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995, Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934. ATP cautions that assumptions, expectations, projections, intentions, plans, beliefs or similar expressions used to identify forward-looking statements about future events may, and often do, vary from actual results and the differences can be material from those expressed or implied in such forward looking statements. Some of the key factors which could cause actual results to vary from those ATP expects include, without limitation, volatility in commodity prices for crude oil and natural gas, the condition of the capital markets generally, as well as ability to access them, the timing of planned capital expenditures, uncertainties in estimating reserves and forecasting production results, operational factors affecting the commencement or maintenance of producing wells, and uncertainties regarding environmental regulations or litigation and other legal or regulatory developments affecting its business. ATP assumes no obligation and expressly disclaims any duty to update the information contained herein except as required by law. While ATP does not file reports with the SEC containing probable and possible reserve quantities, ATP occasionally will include them in news releases, presentations and discuss such reserves publicly. ATP and its independent third party reservoir engineers use the term “probable” to describe volumes of reserves potentially recoverable through additional drilling or recovery techniques that, by their nature, are more speculative than estimates of proved reserves. Any estimates of reserves in this news release have been prepared by our independent third party engineers. More information about the risks and uncertainties relating to ATP's forward-looking statements is found in the company's SEC filings or website, www.atpog.com.

Source: ATP Oil & Gas Corporation

ATP Oil & Gas Corporation, Houston
Chairman and CEO
T. Paul Bulmahn, 713-622-3311
or
Chief Financial Officer
Albert L. Reese Jr., 713-622-3311
www.atpog.com