The all-cash deal with Houston-based TG Natural Resources, which is 70% owned by the Japanese energy firm, is set to be announced this month, the sources said, requesting anonymity as the discussions are confidential. Castleton Commodities International (CCI) owns the rest of TG Natural Resources.

TG Natural Resources is arranging funding from several financing sources to support the transaction, added the sources, who cautioned that no deal was guaranteed and the talks could end without an agreement.

Quantum and CCI declined to comment. Rockcliff and TG Natural Resources did not immediately respond to requests for comment. Tokyo Gas could not be reached for comment outside regular business hours.

Rockcliff produces more than 1 billion cubic feet per day of natural gas from the Haynesville shale formation, which stretches across Louisiana and East Texas. Quantum originally backed the Rockcliff management team with a $350 million investment in 2015.

(Reporting by David French in New York and Shariq Khan in Bengaluru; Editing by Lisa Shumaker)

By David French and Shariq Khan