The United States has some of the richest deposits of shale gas in the world. U.S. lawmakers expressed concern that some chemicals used during fracking, the process used to extract natural gas from shale rock formations, are carcinogenic or otherwise harmful.
A group of what the Platts news service describes as "a coalition of activist shareholder groups" have filed documents trying to get Chevron, Exxon Mobil and Texas company Ultra Petroleum to release information about the fluids used in hydraulic fracturing.
The Environmental Protection Agency in February said eight of the nine companies that practice so-called hydraulic fracturing voluntarily handed over information to help the agency examine the practice. It had to subpoena U.S. energy company Halliburton to hand over its records.
The energy companies targeted by the latest shale measure defended the extraction method.
"Hydraulic fracturing has been used safely over 1 million times in the decades since its first commercial use in the oil and gas industry," Ultra Petroleum said in a statement.
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