The oil and gas drilling practice called hydraulic fracturing has - for the first time - been implicated in the pollution of groundwater supplies in the United States.
New findings from the US Environmental Protection Agency suggest "fracking" could cause contamination, even though the drilling usually takes place thousands of feet below the water table.
Regulators in Colorado have just voted to approve new rules requiring oil and gas companies to disclose most of the chemicals they use in the fracking process.