HOUSTON (

TheStreet

) --

Royal Dutch Shell's

(RDS.A)

U.S. subsidiary has put its South Texas gas fields up for sale, the

Wall Street Journal

reports.

The sale by

Shell Oil

could fetch roughly $1 billion, the

Journal

reports, citing people familiar with the matter.

The most likely buyer for the natural-gas assets is an energy-focused private-equity firm or Master Limited Partnership, the newspaper reports.

Shell's 400 wells in South Texas produce about 210 million cubic feet of natural gas every day, the

Journal

reports, citing information from the company's Web site.

People familiar with the matter described the fields as "mature," meaning that large volumes of gas already have been produced from them, the

Journal

adds.

Shell couldn't be reached for comment.

-- Written by Joseph Woelfel

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