Wachtell Lipton Rosen & Katz, Davis Polk & Wardwell and Sullivan & Cromwell have taken lead roles on the mammoth $34.6bn (£22bn) merger of oil drillers Halliburton and Baker Hughes.

The deal sees the second and third largest oilfield services companies combining in a cash and stock transaction, creating a rival to current market leader Schlumberger.

Wachtell is serving as co-counsel to Halliburton, alongside Baker Botts, with a team headed by corporate partners Daniel Neff and David Katz. The firm is also advising on antitrust aspects of the deal led by New York partner Joseph Larson.

Wachtell's Neff and Katz also secured roles on pharmaceutical giant Actavis' $66bn (£42bn) acquisition of Allergan, announced earlier this week. 

Davis Polk and Wilmer Cutler Pickering Hale and Dorr are acting as joint legal advisors to Baker Hughes on the transaction.

Davis Polk's corporate team includes New York partners Arthur Golden, George Bason and Michael Davis, with the firm also advising on the executive compensation, tax and environment aspects of the deal.

Sullivan & Cromwell corporate partner Stephen Kotran is acting as counsel to Baker Hughes' financial adviser, Goldman Sachs.

Credit Suisse and Bank of America Merrill Lynch are providing financial advice to Halliburton.

The deal is expected to close in the second half of 2015, subject to shareholder and regulatory approval.