ATP Marks Successful Clipper Well Test

ATP Oil & Gas Corporation (NASDAQ: ATPG) today announced the successful completion and testing of the second Clipper well at rates of 9,000 Bbls per day and 4.6 MMcf per day. When combined with the first Clipper well this brings the total test rates to approximately 13.7 MBbls of oil per day and 50.2 MMcf of natural gas per day or 22 MBbls equivalent per day (62% oil).

The second Clipper well is the #4 well located at Green Canyon 300 (GC 300) in the deepwater Gulf of Mexico. The #4 well, located in approximately 3,450 feet of water, logged approximately 56 feet of net oil pay confirming reserves previously booked. The 9-5/8 inch casing was set at 15,778 feet measured depth through the pay intervals. In July 2011, ATP successfully completed and flow tested the first Clipper well, GC 300 #2 ST #1, at a rate of 4,656 Bbls per day and 45.6 MMcf per day.

The pipeline lay barge for the Clipper wells is contracted for third quarter 2012 and will tie in both the GC 300 #4 and #2 wells to the Murphy Oil-operated Front Runner production facility. ATP operates Clipper and presently owns a 100% working interest.

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 timing of planned capital expenditures, availability of acquisitions, uncertainties in estimating reserves and forecasting production results, operational factors affecting the commencement or maintenance of producing wells, the condition of the capital markets generally, as well as ability to access them, 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.