Quicksilver Resources Inc. (NYSE: KWK) plans to sell an undivided 25% interest in its Barnett Shale oil and gas assets for $485 million to TG Barnett Resources LP, a wholly-owned U.S. subsidiary of Tokyo Gas Co., Ltd.

Quicksilver will remain as operator of the assets. Future development spending will be shared in proportion to each party's working interest in accordance with applicable operating agreements. The effective date of the transaction is Sept. 1, 2012. Closing is expected to occur on April 30, 2013 and is subject to customary closing conditions. Proceeds from the transaction are expected to reduce Quicksilver's debt.

"We are very pleased to have Tokyo Gas as a partner to develop the full potential of our Barnett Shale asset base," said Glenn Darden, Quicksilver's president and chief executive. "We look forward to a successful long-term relationship, which will benefit both of our companies."

Quicksilver was advised by Jason Nye of OBV Group LLC, Prairie Bayou LLC, Credit Suisse Securities (USA) LLC and JP Morgan.

Fort Worth, Texas-based Quicksilver Resources is an independent oil and gas company with assets that focus on unconventional reservoirs. Tokyo Gas Co., Ltd., headquartered in Tokyo, Japan, is Japan's largest provider of city gas, serving more than 10 million customers, primarily in the Tokyo metropolitan area and surrounding Kanto region.