NEW YORK (AP) — Billionaire investor Carl Icahn took his case for buying CVR Energy Inc. to its shareholders on Monday, pressing ahead despite management objections and raising the possibility of a proxy fight for control of the company.

Icahn offered to buy CVR Energy for $30 per share in February in a deal valued at $2.6 billion. CVR Energy told its shareholders to reject the offer, calling it "inadequate."

The company argued last week that CVR Energy's management team has delivered shareholder returns of 588 percent over the past three years. But in a letter Monday, Icahn said CVR's management is taking too much credit for a rebound in the company's stock price from its lows in the financial crisis.

The company went public in October 2007 at $19 per share, but fell in late 2008. The stock has since recovered but Icahn said CVR Energy management's attempt to take credit for the big return to shareholders was "a blatant obfuscation of the facts".

CVR has profited from a quirk in the oil markets, not from management's leadership, according to Icahn. And he said CEO Jack Lipinski has had a "dismal performance subsequent to the IPO."

CVR Energy, based in Sugar Land, Texas, issued a statement after the market closed Monday saying that its board has unanimously reaffirmed its decision to reject Icahn's offer. The company said Icahn is extending a "distracting and detrimental campaign" and that his offer still substantially undervalues the company and urged shareholders to reject it.

Icahn argues the company has benefited from a spread in oil prices between global and local U.S. markets. Oil has often been cheaper in the central United States, where CVR Energy buys supplies, than it has been on international markets, according to Icahn. That means CVR Energy has been able to buy oil more cheaply than its competitors on the U.S. coastline, even as it sells refined gasoline at favorable retail prices.

He warned that the price spread won't continue, which could drain CVR Energy's profits. Icahn said the company should be sold, a process that he could execute profitably as he has done in the past.

Icahn extended the deadline of his offer on Friday for CVR Energy shares to April 2 from March 23.

CVR said that contrary to Icahn's criticism of the company and its prospects, that it has a proven track record of delivering outstanding returns and making sound business decisions to increase the value of the business.

"Our record managing this complex business speaks for itself, and we look forward to extending our history of success," CVR's CEO Lipinski said in a statement.

Icahn owns 15 percent of CVR Energy. If he can get another 36 percent by April 2, Icahn said he will have the majority ownership stake he needs for a shareholder proxy fight that could let him replace the board of directors. He said the board he appoints would move the acquisition forward.

"CVR's directors and management are making a huge mistake if they believe I will not consummate this offer immediately if I am given the opportunity," Icahn said.

The company's shares rose 2 cents to close at $27.09 Monday.