Investors are piling into Yahoo stock in the expectation that investor Carl Icahn will force a sale to Microsoft.

Icahn currently owns 50 million Yahoo shares, and has an option for a further 49 million.

Now oil speculator T Boone Pickens has confirmed the purchase of 10 million shares and hedge fund manager Dan Loeb has bought five million.

Pickens said in an interview with CNBC: "I'll jump in with Carl. He goes in first and I jump in behind him."

Pickens made his money in the oil business and was responsible for several large takeovers of oil producers in the 1980s.

More recently he bankrolled the Swift Boat Veterans for Truth, who questioned presidential hopeful John Kerry's Vietnam career in the 2004 presidential elections.

Loeb, meanwhile, runs the Third Point hedge fund based in new York, and is well known for publicly admonishing firms which he feels are being badly run.

Yahoo is gearing up for a major fight and has delayed a crucial board meeting to give itself time to respond to the calls of these new investors to sell the company to Microsoft.