The oil production technique known as fracking has been occurring on offshore platforms and man-made islands off some of Southern California's most populous coastal communities.
Interviews and drilling records obtained by The Associated Press show fracking has occurred at least 200 times over the past two decades in waters off Long Beach, Seal Beach and Huntington Beach.
Though there is no evidence offshore hydraulic fracturing has led to any spills or chemical leaks, the practice occurs with little state or federal oversight of the operations
The state agency that leases lands and waters to oil companies says officials found new instances of fracking after searching records as part of a review after the AP reported this summer about fracking in federal waters of California.
Explore further: Calif. panel launches probe into offshore fracking