U.S. lawmakers of the Republican party have charged that over regulation has prevented a shale oil boom in California and that easing the rules could boost production in the state and reduce its dependence on foreign energy.

With more than an estimated 15 billion barrels of oil, according to the U.S. Energy Information Administration, California's Monterey shale formation is twice as large as North Dakota's Bakken formation. That state has risen to become the second-largest U.S. oil producer in recent years, behind Texas.

California had the third-largest U.S. oil output in 2013, narrowly ahead of Alaska, but could produce far more if the state aggressively moved to develop its energy resources, the Republican lawmakers said at a House Natural Resources committee hearing.

"The challenge now is not our ability to find it, it's the ability of government allowing us to be able to produce it in a sound way," said Kevin McCarthy, who represents California's oil-producing Kern county.

Mostly cut off from the rest of the U.S. oil production, California relies on countries such as Iraq and Saudi Arabia to meet more than half of its crude oil needs.

State regulators are working to update oversight of hydraulic fracturing, or fracking, the drilling technique that has helped to spur the U.S. shale oil and gas boom.

Uncertainty surrounding future energy policies and lengthy permitting processes have pushed energy companies away from California, Jean Fuller, a California Republican state senator, told the hearing.

Critics of fracking, have blamed the practice for water contamination and have raised concerns that increased drilling has polluted the air.

California Democrats at the hearing pushed back against claims that the state's stringent environmental rules have harmed the state.