ATP Adds Two New Producing Wells in the Gulf of Mexico

ATP Oil & Gas announced first production from its Matagorda Island 709 A-4 ST-1 (MI 709 A-4 ST-1) well and its High Island 74 No. 1 (HI 74) well. The MI 709 A-4 ST-1 well, located in 145 feet of water, was completed in an upper Miocene Marg A sand at 9,715 feet TVD. The MI 709 A-4 ST-1 is the third currently producing well at the Company's Matagorda 704/709 complex. ATP operates MI 709 with a 62.5% working interest. The HI 74 No. 1 well, located in 41 feet of water, was completed in Miocene Rob L sand at 8,760 feet TVD. ATP operates HI 74 with a 75% working interest. The completion and first production from the High Island 74 property enhances the success ratio to 38 out of 39 properties brought from a proved undeveloped status to production, an ATP successful completion record of 97%. With the addition of the wells at High Island and at Matagorda Island, ATP has placed four new wells on production in 2005.

Other operations continue at several ATP Gulf of Mexico and North Sea projects. These projects in the Brazos, Eugene Island and West Cameron areas of the Gulf of Mexico and in the Dutch sector of the North Sea are on schedule to contribute to ATP's production beginning in the 3rd and 4th quarters of this year. At the Company's Mississippi Canyon 711 project, rig operations began on May 4, 2005 with anchoring of the rig and installation immediately thereafter of tubing head adapters on each well. Due to presently excessive loop currents in the Mississippi Canyon area, ATP at 7 p.m. CT on May 20th temporarily released the Ocean Voyager rig. It is expected to return in sufficient time so as to not impact the estimated fourth quarter 2005 startup of the Mississippi Canyon project.

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