Gastar Exploration Inc. (NYSE MKT: GST) will offer 40 million common shares in a public offering, the company said May 11.

Underwriters will receive a month-long option to purchase 6 million additional shares.

Net proceeds will support general corporate purposes, including funding an expanded drilling program on its Oklahoma Stack Play acreage.

Seaport Global Securities LLC and Johnson Rice & Co. LLC are joint book-running managers.

Gastar Exploration Inc. is based in Houston.