Roman Abramovich, the Russian tycoon who last year bought Chelsea Football Club, could be set to scoop $10bn (£5.6bn) from the sale of his stake in Russian oil company, Sibneft.
It is thought that Sibneft has held informal talks with at least three Western oil majors, including Shell. Mr Abramovich, a Russian "oligarch", has been liquidating his assets in the country but the Sibneft deal would dwarf these other disposals.
Analysts cautioned, however, that there were significant legal and political hurdles for Mr Abramovich to cross before he can realise the value of his holding. Firstly, he must reverse a merger with the larger rival, Yukos, that has already been through the courts in Russia - a process now under way.
Stephen O'Sullivan, the head of research at United Financial Group - a Moscow broker - valued Sibneft at $22bn, making Mr Abramovich's stake in the company worth nearly $10bn.
Mr O'Sullivan said: "I have no doubt that everyone is keeping their lines open to Sibneft."
Adam Landes, an analyst at Renaissance Capital, said Russia was too compelling a source of oil and gas outside Opec for Western majors to ignore.
Sibneft is believed to have held talks with Shell, ChevronTexaco of the US and France's Total. It is thought that Exxon would also be interested in Sibneft, if it cannot pull off its preferred acquisition of Yukos.
Mr Landes said: "If they [Sibneft] can break the Yukos deal, they would be a willing set of sellers. They have been leaking for ages that they want to sell. That is why they did the Yukos deal [last year]. Before that, they were talking to foreign companies."
It is understood that Sibneft negotiated with Shell and Total before it settled for Yukos as a merger partner, in what proved to be an ill-fated deal. Just as the merger was completing, the Russian government arrested the chief executive of Yukos, who remains in prison on fraud and tax evasion charges.
Sibneft has decided to try to unwind the Yukos merger - even though it had technically completed - in the face of fierce resistance from Yukos. A recent Russian court decision, which disqualified the Yukos shares that were paid over to Sibneft as part of the transaction, has given hope to the Abramovich side.
Mr O'Sullivan said that any deal would need to get the blessing of the government of the Russian President, Vladimir Putin, and Mr Abramovich's relations with the Kremlin appear to have remained good.
"Abramovich has not fallen foul of anyone in the Kremlin," he said.
It is thought that Mr Abramovich owns some 46 per cent of Sibneft but including the shareholder of his associates, he speaks for up to 94 per cent of the shares in the company. Analysts said that any Western company would be interested in a transaction only if it would come with over 50 per cent of Sibneft shares.
A Sibneft spokesman said: "At the moment we are focusing on the demerger with Yukos and its too early to comment on what might happen in the future."