John Thomas, general counsel and corporate secretary of Crimson Exploration Inc., is using Vinson & Elkins for the Houston-based company’s pending acquisition by Contango Oil & Gas Co. in a deal valued at $400 million.

Contango, an independent oil and gas company based in Houston, turned to lawyers from Morgan, Lewis & Bockius.

On April 30, Contango and Crimson announced a merger agreement for an all-stock transaction through which Crimson would become a wholly owned subsidiary of Contango. Once the merger is complete, shareholders of Crimson stock would receive 8.288 percent of a share of Contango stock for each share of Crimson stock they own. Contango will assume about $244 million in Crimson debt as a part of the deal.

The merger must be approved by shareholders of Contango and Crimson and meet customary closing conditions. It is expected to close during the third quarter of 2013.

Mergers-and-acquisitions partner Stephen Gill of Houston leads the V&E team for Crimson, with assistance from M&A partners James Prince and Mark Kelly and associates Kai Liekefett, James Garrett, Bobak Fatemizadeh and Kelly Sanderson. Others from V&E include employee benefits partner David D’Alessandro and associate Missy Spohn and oil and gas associates John Grand and Scott Fulford, all of Dallas; labor/employment partner Sean Becker, environmental counsel Larry Pechacek, tax partner John Lynch, all of Houston; and Washington, D.C.-based antitrust partner Billy Vigdor.

At Morgan Lewis, business and finance partners Richard Shortz of Los Angeles and Richard Aldridge of Philadelphia led Contango’s team. Others include securities partner David Sirignano of D.C., business and finance associates Vanessa Kwong of Los Angeles, Andrew Mariniello, Kate Moll-Taylor and Robert Brown, all of Philadelphia, and Peter Hays of Houston; business transactions associate David Chang of Los Angeles; employee benefits and executive compensation partner Mims Zabriskie and tax partner Paul Gordon, both of Philadelphia; antitrust partner Harry Robins of New York, and litigation partners Marc Sonnenfeld and Elizabeth Fay, both of Philadelphia.

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