Oneok ( OKE) agreed to sell a group of natural gas gathering and processing assets in Texas to Eagle Rock Energy, a privately held company based in Houston. The transaction, valued at $528 million, is scheduled to close Dec. 1. The properties are located in the Texas Panhandle and include six gas processing plants, around 3,700 miles of gas gathering lines and estimated natural gas liquid production of 13,500 barrels a day. Oneok plans to use the proceeds from the sale to buy other assets or to pay off debt. The company estimated the after-tax proceeds at $356 million. Oneok, a Tulsa-based energy company, will record a book gain of around $162 million in the fourth quarter.