Slaughter and May and a line-up of top US law firms have advised on the merger of offshore drilling companies Ensco and Rowan Companies, a deal that creates a combined company valued at $12bn.

Ensco will acquire 100% of Rowan's stock by way of a court-sanctioned scheme of arrangement, with Ensco shareholders owning 60.5% and Rowan's owning 39.5% of the combined business.

Slaughters is advising Ensco, fielding a team headed up by corporate partners Hywel Davies and Christian Boney, together with competition partner William Turtle, pensions partner Jonathan Fenn and tax partner Mike Lane.

The magic circle firm is working alongside Gibson Dunn & Crutcher, which is handling US aspects of the deal with a team led by corporate partner Tull Florey and tax partner David Sinak.

The two firms worked closely with Ensco general counsel Michael McGuinty and senior legal counsel Davor Vukadin.

Meanwhile, Kirkland & Ellis and Latham & Watkins acted for Rowan, with Kirkland deploying a transatlantic team led by Houston-based corporate partners Sean Wheeler, Doug Bacon, Dallas-based partner Ryan Gorsche, and City partners David Higgins, David Holdsworth and Dipak Bhundia, as well as New York-based executive compensation partner Scott Price and tax partners David Wheat, Lane Morgan and Mike Carew.

For Higgins, it represents the latest big-money deal he has worked on since his move from Freshfields Bruckhaus Deringer last year, after his recent role on the sale of eastern European media and communications company United Group to private equity house BC Partners for a reported €2.6bn (£2.3bn).

Latham is advising Rowan on the antitrust and anti-corruption aspects of the deal, fielding a team consisting of Washington DC corporate partner Michael Egge, Brussels managing partner Lars Kjolbye, and London partner Jonathan Parker.

Morgan Stanley acted as lead financial adviser to Ensco, with HSBC Securities and Citigroup Global Markets supporting, while Rowan turned to Goldman Sachs. Cleary Gottlieb Steen & Hamilton partners Ethan Klingsberg and  James Langston advised Goldman out of the firm's New York base.

Slaughters last year advised Ensco on its proposed acquisition of fellow offshore drilling company Atwood Oceanics, and the firm has taken on several mandates in the oil and gas sector in recent years, including on a joint venture deal between Centrica and Oslo-based oil and gas company Bayerngas Norge last year, and the $13bn (£11bn) acquisition of India's Essar Oil by a group led by Russia's Rosneft in 2016.

The deal, which is expected to complete in early 2019, is subject to shareholder approval, as well as court and regulatory approval.