SHAREHOLDER ALERT: Brower Piven Informs Investors With Substantial Losses From Investment In ATP Oil & Gas Corporation That Less Than Three Weeks Remain To Seek Appointment As Lead Plaintiff In Securities Class Action Lawsuit

Brower Piven, A Professional Corporation announces that a class action lawsuit has been commenced in the United States District Court for the Southern District of Texas on behalf of purchasers of ATP Oil & Gas Corporation (“ATP” or the “Company”) (OTC: ATPAQ) common stock during the period between December 16, 2010 and August 17, 2012, inclusive (the “Class Period”).

If you have suffered a net loss from investment in ATP Oil & Gas Corporation common stock purchased on or after December 16, 2010, and held through any of the revelations of negative information on August 10, 2012 and/or August 17, 2012, as described below, you may obtain additional information about this lawsuit and your ability to become a lead plaintiff by contacting Brower Piven at www.browerpiven.com, by email at hoffman@browerpiven.com, by calling 410/415-6616, or at Brower Piven, A Professional Corporation, 1925 Old Valley Road, Stevenson, Maryland 21153. Attorneys at Brower Piven have combined experience litigating securities and class action cases of over 60 years.

No class has yet been certified in the above action. Members of the Class will be represented by the lead plaintiff and counsel chosen by the lead plaintiff. If you wish to choose counsel to represent you and the Class, you must apply to be appointed lead plaintiff no later than October 4, 2013 and be selected by the Court. The lead plaintiff will direct the litigation and participate in important decisions including whether to accept a settlement and how much of a settlement to accept for the Class in the action. The lead plaintiff will be selected from among applicants claiming the largest loss from investment in the Company during the Class Period.

The complaint accuses the defendants of violations of the Securities Exchange Act of 1934 by virtue of the defendants’ failure to disclose the impact that two successive United States Department of the Interior moratoria for deepwater drilling operations in the Gulf of Mexico had on the Company’s operations and revenues and the Company’s breach of certain credit agreements by engaging in disguised financing arrangements that were designed to evade the requirements of such credit agreements. According to the Complaint, following reports on August 10, 2012 that the Company might file for bankruptcy and the Company’s August 17, 2012 disclosure that it was filing for Chapter 11 bankruptcy, the value of ATP shares declined significantly.