Three big law firms with energy practices—Vinson & Elkins, Gibson Dunn & Crutcher and Davis Polk & Wardwell—have landed roles on private equity firm First Reserve’s pending $1.225 billion sale of its Deep Gulf Energy Cos. to Dallas-based Kosmos Energy.

Gibson Dunn represents First Reserve, a Stamford, Connecticut-based  global private equity investment firm focused on energy, while V&E is advising Deep Gulf Energy, which runs deepwater oil and gas exploration and development projects in the Gulf of Mexico. Kosmos, a deepwater oil and gas company, turned to Davis Polk.