Linklaters, Allen & Overy, Vinson & Elkins, and Indian firms AZB & Partners and Talwar, Thakore & Associates are advising on the $7.2 billion deal that will see BP plc acquire a 30 percent interest in offshore oil and gas fields held by India’s Reliance Industries Ltd. The two companies will form a 50-50 joint venture to source and market natural gas.

In addition, BP has also agreed to pay Reliance performance bonuses of up to $1.8 billion, depending on the success of future exploration in those fields. Those payments, along with future investments, could eventually bring the total value of the deal to $20 billion.

“India is one of the fastest growing economies in the world,” said BP Group Chief Executive Robert Dudley, in a statement. “By allying ourselves with Reliance, we will access the most prolific gas basin in India and secure a place in the fast growing Indian gas markets, creating a genuinely distinctive BP position.”

Magic Circle firm Linklaters is representing BP in the deal, with India head Sandeep Katwala and corporate partner Stephen Griffin, both based in London, leading the team.

“This transaction is historic in that it marks a strategic partnership between one of India’s largest companies and one of the world’s leading oil companies,” says Katwala. “To date international players have generally not made significant investments in Indian exploration and production. Potentially this could encourage other foreign investors.”

India’s Talwar, Thakore–“best friends” with Linklaters since 2007–assisted on the due diligence, drafting and negotiation of the transaction documents for BP. The Mumbai-based firm is also providing advice on Indian regulatory requirements.

Reliance is looking to Allen & Overy, AZB & Partners, and Vinson & Elkins. Allen & Overy’s team is being led by London-based energy partners John Geraghty and Paul Griffin, with specialist antitrust advice provided by London partner Mark Friend.

“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,” said Geraghty in a statement.

Vinson & Elkins was co-counsel with Allen & Overy. Partners James Cuclis and Gary Kotara, both based in Hong Kong, led the firm’s work on the deal. Beijing partner Paul Deemer also played a role in the deal; he and Kotara have developed Vinson & Elkins’s 15-year relationship with Reliance. Last year, the firm also represented the Indian company on its $1.7 billion JV with Pennsylvania-based Atlas Energy.

“There was no real China aspect on this deal, just that the relevant relationship partners were based there,” says Cuclis, who says that most of Vinson & Elkins’s India work is coordinated from Hong Kong.

AZB Mumbai partner Shuva Mandal is advising Reliance on regulatory issues, as well as the documentation and negotiation of the sale and purchase agreements and the joint venture. Former Clifford Chance alliance partner AZB last August advised on Reliance’s $217 million acquisition of a 14 percent stake in the Oberoi hotel and resort chain.

Reliance in-house counsel Atul Dayal and Naveen Raju oversaw the outside firms’ work.

This deal is BP’s second major investment this year, just after its recent $7.8 billion agreement with Russian state-controlled oil company Rosneft to drill in the Arctic Ocean–a deal in which the oil giant was also advised by Linklaters, along with Baker & McKenzie.