NEW DELHI (BLOOMBERG) - Indian billionaire Mukesh Ambani's Reliance Industries Ltd. is weighing a sale of its U.S. shale gas investments, people with knowledge of the matter said.

The Mumbai-based company may sell the holdings as part of a strategic review of its assets, as it believes their worth isn't fully reflected in its market value, one of the people said, asking not to be named as the details are private. It has invested more than US$8 billion in its unconventional gas joint ventures through the end of March, according to its annual earnings report.

Reliance, the operator of the world's biggest oil-refinery complex, said July 24 that earnings from its shale assets fell in the latest quarter as natural gas prices slumped. Hydraulic fracturing has opened up reserves from Texas to North Dakota, causing prices to fall 54 pe rcent from the five-year high reached in 2014.

Selling the shale assets would allow Reliance to put its capital to more productive uses, given the gas market may not improve for some years, according to one of the people. It hasn't made a final decision to sell, and Reliance isn't willing to part with the assets at a depressed price, another person said.

BHP Billiton Ltd. wrote down an additional US$2.8 billion on its shale assets this month, joining impairments by explorers Royal Dutch Shell Plc, Statoil ASA and Total SA. Tushar Pania, a spokesman for Reliance, didn't reply to an e-mail seeking comment.

Reliance, which has a market value of US$51 billion, owns 45 per cent of a project controlled by Pioneer Natural Resources Co. in south Texas's Eagle Ford formation. It also has a 40 per cent interest in a Chevron Corp. venture in the Marcellus shale deposit in Pennsylvania, as well as 60 per cent of a project in the same area jointly owned with Carrizo Oil & Gas Inc.

The Indian company and partner Pioneer Natural Resources this month sold a Texas pipeline and processing company to Enterprise Products Partners LP for US$2.15 billion.