Item 1.01. Entry into Material Definitive Agreement.

On June 11, 2009, ATP Oil & Gas Corporation (the "Company") entered into an Underwriting Agreement with J.P. Morgan Securities Inc., as representative of the several underwriters named in Schedule 1 of the Underwriting Agreement (collectively, the "Underwriters"), relating to the issuance and sale of 8,750,000 shares of common stock, par value $0.001 per share, of the Company (the "Shares"). The Underwriters were also granted an option to purchase up to an additional 1,312,500 Shares. The offering of the Shares was registered under the Securities Act of 1933, as amended, pursuant to the Company's Registration Statement on Form S-3 (Registration No. 333-159614) filed with the Securities and Exchange Commission on May 29, 2009, as amended by a pre-effective amendment filed on June 9, 2009. The offering is expected to close on June 17, 2009, subject to customary closing conditions.

A copy of the Underwriting Agreement is filed as Exhibit 1.1 to this Current Report on Form 8-K and the contents thereof are incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits.

1.1 Underwriting Agreement dated June 11, 2009 among the Company and J.P. Morgan Securities Inc., as representative of the several Underwriters named therein.

---