The Brown administration on Tuesday released draft regulations that would require oil companies for the first time to disclose where in California they use hydraulic fracturing, a controversial but little regulated method of oil extraction.

The proposed rules, issued by the state Department of Conservation, were immediately criticized by environmentalists as too lenient.

Hydraulic fracturing, or fracking, in which water and chemicals are injected underground to break up rock formations, has been used for decades in California – safely, oil producers say. Environmentalists have said the method of oil extraction can damage wells and pollute groundwater.

The draft regulations would require oil producers to test the integrity of wells they intend to use for hydraulic fracturing before drilling, to provide advance notice to the state and to monitor sites where hydraulic fracturing is employed. The regulations would also require drillers to disclose the chemical makeup of the fluid they use in hydraulic fracturing, though it would provide an exemption in cases in which an operator claims the fluid makeup is a trade secret. The Environmental Working Group and Center for Biological Diversity's Climate Law Institute in San Francisco both criticized the proposed trade secret exemption.

"Experience in other states has shown that such trade secret exemptions are being widely used and likely abused," the Environmental Working Group's Bill Allayaud said in a prepared statement.

Regulators said trade secrets are not widely claimed in other states.

Jason Marshall, chief deputy director of the Department of Conservation, said the proposed regulations constitute a "discussion draft." The administration's formal rule-making process could take a year.

The draft rules follow calls by lawmakers and environmentalists for the state to regulate hydraulic fracturing. The Western States Petroleum Association, a major industry group, announced in May that its members would voluntarily post information about hydraulic fracturing operations on a disclosure website, Frac Focus. The proposed regulations would require such disclosure.

It is unclear exactly how prevalent hydraulic fracturing is in the Golden State. When it announced its voluntary measure earlier this year, the Western States Petroleum Association said the process was used in 628 of California's tens of thousands of wells last year by member companies.

Those companies represent about 80 percent of all oil production in the state. Most of the hydraulic fracturing occurs in Kern County. In California, the process is most commonly used for oil; in other states, its use for natural gas has created controversy.