Linklaters and Freshfields Bruckhaus Deringer have taken lead roles on a multibillion-pound strategic partnership between BP and Russian energy giant Rosneft.

Linklaters advised longstanding client BP on the $16bn (£10.1bn) share swap backing the deal, which will see the UK company take a 9.5% stake in Rosneft, worth around $8bn (£5bn).

Rosneft, Russia's largest energy company, will take a 5% stake in BP, backing an equity-linked partnership to pursue joint projects in the Russian Arctic shelf.

Linklaters fielded a team led by London-based corporate partner Stephen Griffin, who worked alongside corporate partner Grigory Gadzhiev in Moscow.

Freshfields, meanwhile, advised the state-controlled Rosneft on the joint venture, fielding a team led by London-based corporate partner Sebastian Lawson and Moscow-based corporate associate Sergei Diyachenko.

The deal is linked to Rosneft's initial public offering, under which the company is offering shares to strategic allies such as BP as well as international investors and the Russian retail market at $7.55 (£4.75) per share. At the offer price the company is valued at almost $80bn (£51bn).

Two other strategic investors are buying more than 5% of the shares on offer, with China's CNPC acquiring $500m (£315m) worth of shares and Malaysia's Petronas reported to have bought a similar amount.

The mandate will be seen as welcome for Linklaters. Despite its long-time reputation as one of BP's leading advisers, recent months have seen Freshfields and CMS Cameron McKenna take on several significant instructions for the UK energy giant.

The deal is also the first major strategic play from BP since the UK oil firm became embroiled in the Deepwater Horizon spill in 2010, which is expected to ultimately cost the company around $40bn (£25bn). The Rosneft JV is also expected to be examined closely in the US, where BP is a major supplier.