Icahn increased his ownership to about 5 percent from 2.5 percent, according to the filing with the U.S. Securities and Exchange Commission. He has already had discussions with company officials about Chesapeake’s operations and “the maximization of shareholder value,” according to the filing, which was released after the close of trading Friday.

On Dec. 15, Icahn agreed to buy Dynegy Inc., the third- biggest U.S. independent power producer, for $665 million, outbidding Blackstone Group LP.

Oklahoma City-based Chesapeake’s stock has fallen 10 percent this year as gas prices have declined. The company announced plans this year to shift its production away from gas and into crude oil.