Activist investor Carl Icahn announced Thursday he was sweetening a takeover offer for independent petroleum refiner CVR Energy Inc. (NYSE:CVI), proposing to buy all outstanding shares of the company, in cash, at $30 a share.

The amount being offered represents a premium of 5.59 percent over where shares were trading prior to the announcement, and more than 30 percent since Icahn's interest in Sugar Land, Texas-based CVR was announced. He owns 14.54 percent of outstanding shares.

We are launching this tender offer and proxy fight to provide shareholders the opportunity to obtain the value that we believe can be obtained in a sale of the Company, Icahn said in a statement. We are offering shareholders a minimum of $30 per share now, a new board with a shareholder mandate to put the Company up for sale

The statement also noted shareholders who sell would be offered a Contingent Value Right agreement, which would pay them for any appreciation their sold shares experience in the event the company is resold by Icahn within nine months.

This is a win-win-win for shareholders, Icahn said.

Icahn's stated plan is to resell CVR to a competitor after acquisition. He has said he believes the company could fetch some $37 a share in such a scenario.

Shares of CVR Energy spiked on the news, and were recently trading at $29.52, up 6.96 percent from the previous day's close.