Magic circle duo Linklaters and Allen & Overy (A&O) have won lead roles as BP enters into a joint venture (JV) deal representing one of the largest-ever foreign direct investments into India.

Linklaters is advising regular client BP on the $7.2bn (£4.4bn) JV that sees it tie up with Indian energy giant Reliance Industries, which was advised by A&O.

A&O's team was led by high-profile energy partners John Geraghty and Paul Griffin – who joined the magic circle firm from Herbert Smith last year – and also included antitrust partner Mark Friend.

Reliance also instructed Texas energy firm Vinson & Elkins as co-counsel to A&O on the transaction, as well as former Clifford Chance best friend firm AZB Partners, which provided local law advice.

Linklaters floated a team led by the firm's India group head Sandeep Katwala and fellow London-based corporate partner Stephen Griffin. Linklaters' Indian best friend firm Talwar Thakore & Associates acted as Indian legal adviser to BP.

Geraghty said: "This is a landmark transaction by any measure and strategically important for Reliance. We have a much valued relationship with Reliance and it is fantastic that we have been able to continue to develop that relationship by advising them in relation to this deal."

In return for its investment BP will gain a 30% stake in 23 oil and gas production sharing contracts that Reliance operates in India, with the deal also including a 50:50 joint venture between the two companies for sourcing and marketing gas in India.

Future performance payments and investment from both companies could mean a total combined investment in India of up to $20bn (£12.3bn).