Rosneftdoubled up its bet on BP’s Russian joint venture yesterday, agreeing to pay $55bn for 100 per cent of the oil producer in a deal that will make it the world’s largest publicly traded energy company and tighten the Kremlin’s grip on the Russia’s energy sector.

Rosneft will buy out both of TNK-BP’s current owners – BP and a consortium of oligarchs known as Alfa-Access-Renova– in the largest global mergers-and-acquisitions transaction since 2010 and the biggest oil industry transaction in a decade. The deal catapults Rosneft into the premier league of international oil majors with production of 4.6 million barrels of oil equivalent a day – way ahead of listed rivals such as PetroChina and ExxonMobil.

BP will take nearly 20 per cent of Rosneft, making it the second largest shareholder in the national energy champion after the Russian state and giving it two seats on the company’s board. It could also help to ensure BP’s future in Russia for decades to come, potentially giving the UK group access to some of the world’s largest untapped oil and gas resources. In a statement, Rosneft chief executive Igor Sechin said his company would “benefit from BP’s experience and?.?.?.?record of implementing best international practices in Russia”.