Companies prospecting for oil off California's coast have used hydraulic fracturing on at least a dozen occasions to force open cracks beneath the seabed, and now regulators are investigating whether the practice should require a separate permit and be subject to stricter environmental review. FILE - In this May 1, 2009 file photo, offshore oil drilling platform 'Gail' operated by Venoco, Inc., is shown off the coast of Santa Barbara, Calif.