The deal with Reliance Industries, potentially worth up to $20bn and subject to government approval, comes on the heels of a $16bn share swap with Rosneft, the Russian state oil company, and marks the latest stage of BP's recovery since last year's Gulf of Mexico disaster.It also represents an endorsement of the prospects for continued rapid expansion of the world's second-fastest growing major economy.
"This partnership will help unlock the huge potential of India's vast but under-explored acreages," Mr Ambani told reporters while unveiling the deal with Bob Dudley, BP chief executive, in London, ahead of a planned signing ceremony at 10 Downing Street with George Osborne, UK chancellor.
The deal is the biggest foreign investment in Indian energy and among the largest in any sector.
It further cements Anglo-Indian business ties, following Vodafone's $10.7bn purchase of a 67 per cent stake in what became Vodafone Essar, India's third biggest mobile operator, in 2007.
Mr Ambani, whose energy interests form the backbone of a conglomerate that has made him a fortune estimated by Forbes to be the world's fourth largest at $29bn, said BP's technical expertise would "accelerate" exploration.
All 23 blocks lie offshore, mainly off India's east coast and at depths ranging from 400m to more than 3km.
The Indian group's current output of 1.8bn cubic feet of gas per day -- 40 per cent of India's gas production -- comes from the sole block that is in production.
BP agreed to pay an initial $7.2bn and additional performance-related payments of up $1.8bn. These payments and combined investment could amount to $20bn, the companies said.
"Reliance is a newcomer in this upstream business so it required a more experienced partner that could provide them the technology needed to extract deepwater oil and gas," said an analyst with a global ratings agency.
The tie-up aims to supply the domestic market, where natural gas accounts for a small but growing share of energy consumption. BP forecasts that demand will more than double over the next 20 years.
The courtship between the two groups goes back five years. Since 2008 BP has operated a 50-50 joint venture with Reliance developing an offshore Indian oil block.
