ATP Oil & Gas Corp. ATP Oil & Gas Corporation engages in the acquisition, development, and production of oil and natural gas properties, focusing on proved undeveloped reserves in mature offshore areas; its core assets include leasehold interests in multiple blocks and subsea wells in the U.S. Gulf of Mexico and the U.K. North Sea, encompassing approximately 78.6 million barrels of crude oil or liquid hydrocarbons and 241.5 billion cubic feet of natural gas reserves as of its last reported figures, with additional historical interests in deepwater licenses off Israel. The company targets properties economically viable for development but overlooked by larger exploration firms, operating through subsea tie-backs to existing infrastructure to minimize exploration risks; it serves oil and gas markets in the Gulf of Mexico, North Sea, and served end-users via pipelines and processing platforms. Founded in 1991 by T. Paul Bulmahn and headquartered in Houston, Texas, with additional offices in Guildford, United Kingdom, and IJmuiden, Netherlands, ATP Oil & Gas historically maintained a 98% success rate in bringing undeveloped projects to production. In August 2012, the company filed for Chapter 11 bankruptcy protection in the U.S. Bankruptcy Court for the Southern District of Texas (case no. 12-36187), citing $3.49 billion in debts against $3.64 billion in assets amid post-Deepwater Horizon drilling restrictions and high leverage, leading to operational wind-down, asset sales including to Bennu Oil & Gas, and conversion to Chapter 7 liquidation by October 2021, rendering it defunct with no current operations or trading activity.