A line-up of magic circle and US law firms have taken lead roles on BP's $10.5bn (£8bn) acquisition of BHP Billiton's US shale oil and gas business.

The purchase of issued share capital of Houston-based Petrohawk Energy Corp., the BHP subsidiary that owns the Eagle Ford, Haynesville and Permian assets, is BP's largest acquisition in almost two decades and will give the oil and gas company access to extensive resources in Texas and Louisiana.

MMGJ Hugoton III, which is owned by Merit Energy Company of Dallas, will also buy BHP's Arkansas and Fayetteville interests for $300 million (£228.2m).

Freshfields acted for BP on English law aspects of the deal, with a team led by London managing partner Julian Long, co-heads of natural resources Sam Newhouse and Julian Makin, and tax partner May Smith. The role comes after the magic circle firm was reappointed to BP's panel in December last year.

US firm Foley & Lardner acted for BP on American law issues, with Houston-based energy partners Timothy Spear and Eunice Song leading the firm's team.

A Locke Lord team advised Merit with a team fielded by Dallas partner Van Jolas, with assistance in Houston from tax partner Ed Razim and environmental partner Jerry Hidgon, in Dallas from employment partners Paul Nason, capital markets partner Jason Schumacher, corporate partner Will Becker and tax partner Geoff Polma, and in Austin from corporate partner Michelle Earley and Washington DC energy partner Tom Knight.

Slaughters advised BHP on English law with a team led by corporate partner Richard de Carle, while Baker Botts took the US role for the company, with a Houston-based team including global projects head Jason Bennett, firmwide chair of the environmental department Scott Janoe, projects partners Erin Hopkins and Craig Vogelsang, and tax partners Jon Lobb and Rob Fowler.

The deal, which is subject to regulatory approvals and is expected to close by the end of October, was described by Baker Botts' Bennett as "one of the most significant transactions in the oil and gas upstream market in a number of years".

MMGJ Hugoton III, which is owned by Merit Energy Co. of Dallas, will buy 100 percent of the issued share capital of BHP Billiton Petroleum (Arkansas) and all of the membership interests in BHP Billiton Petroleum (Fayetteville), which hold the Fayetteville assets, for $300 million.

For BP, the transaction comes after its acquisition of Chargemaster – the UK's biggest electric car charging network – this July, a deal which saw Herbert Smith Freehills (HSF) advise BP alongside CMS.

HSF, CMS and Freshfields were among 18 law firms appointed by BP to its new panel last December, alongside Addleshaw Goddard, Ashurst, Baker McKenzie, HFW, Linklaters, Norton Rose Fulbright, Pinsent Masons, Simmons & Simmons and Three Crowns.

Atma Partners, Dentons, Euclid, Hill Dickinson, Hogan Lovells and PwC Legal were added to the roster, which went live in January 2018 and will be in place for three years.