SOFIA, Bulgaria—Bowing to public pressure, Bulgaria's government says U.S. oil company Chevron cannot explore for shale gas in the country using the extraction technique known as "fracking."

Energy Minister Traicho Traikov said that under Tuesday's decision "Chevron can still have the right to test for oil and gas, but without using the controversial technology of hydraulic fracturing."

He says San Ramon, California-based Chevron had not yet been notified of the decision and negotiations on the contract are pending.

Over the last weeks, thousands of people gathered at protest rallies across Bulgaria to protest against shale gas extraction and the use of fracking, fearing it could have a hazardous impact on the environment and people's health.

Last June, Bulgaria granted U.S. oil company Chevron a permit to explore for shale gas in the northeastern part of the country. The potential reserves of shale gas in this area -- the country's main grain producing region -- are estimated at up to 1 trillion cubic meters.

Bulgaria, which is almost totally dependent on Russian gas supplies, has long pushed for a way to diversify its energy sources, including shale gas. It has said Chevron would prepare a five-year project worth euro50 million ($72 million) and invest euro4 million ($5.8 million) on environment protection.

Traikov explained that it was not possible to drill for shale gas with the permits already issued. He added that companies were required to submit a working program setting out the method of extraction, which had to pass various environmental impact assessments before it could be approved conclusively.

On Wednesday, Parliament is scheduled to vote a proposal on a total ban on hydraulic fracturing in Bulgaria and its Black Sea territorial waters. The draft was made by the ruling center-right GERB party and is expected to be approved with a comfortable majority.

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