Gastar Exploration Ltd. is buying proven reserves and undeveloped leasehold interests in Oklahoma from Chesapeake Energy Corp. for $75.2 million.The oil and natural gas company also agreed to repurchase Chesapeake's shares of its stock for $9.8 million and to settle all litigation between the companies.Gastar shares rose more than 11 percent in premarket trading Monday.Gastar said that the acquisition includes 176 producing wells with an estimated present value of proved reserves of $32.4 million. The proven reserves and undeveloped leasehold interests are in Kingfisher and Canadian counties in Oklahoma.Gastar President and CEO J. Russell Porter said in a statement that the acquisition will give Gastar the chance to secure a much larger position in what it feels has the potential to be a highly prolific oil field.Gastar also agreed to repurchase from Chesapeake about 6.8 million shares of Gastar's stock at $1.44 per share. This is Chesapeake's entire stake in Gastar and is about 9.9 percent of Gastar's total outstanding stock.The companies have also agreed to settle all current litigation between them. Chesapeake filed a lawsuit against Gastar in October in the U.S. District Court for the Southern District of Texas seeking rescission of some 2005 transactions with Gastar and reimbursement of additional well costs.