US Asks Firms to Reveal Gas Extraction Liquid (Agence France Presse)

US companies have increasingly tapped shale gas, which lies deep underground and was once thought inaccessible. Firms force out the gas through hydraulic fracturing, or fracking, in which a large volume of liquid is injected below.

The Environmental Protection Agency said it had sent letters to nine companies including energy giant Haliburton asking for data within 30 days on the chemicals involved in fracking.

The agency's chief, Lisa Jackson, said the data would "help us make a thorough and efficient review of hydraulic fracturing and determine the best path forward."

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