US oil giant Chevron obtained zoning certificates in eastern Romania enabling it to explore for shale gas, despite controversy about the effect of drill fracking on the environment, local authorities said on Thursday.

"We have delivered the certificates because this is what legislation requires us to do," the head of Vaslui county council Dumitru Buzatu told AFP.

The US group had "on several occasions applied for the certifcates and a refusal on our part would have been an abuse," he added.

Fracking is a process whereby liquid products, including water, are pumped deep into oil or gas-bearing rock to cause fractures and thereby release hydrocarbons.

The next step for the company is to obtain a contruction permit before it can start exploration drilling, Buzatu said.

"Chevron continues to work with the Romanian government to permit and execute activities within concession areas", the company told AFP, stressing all its activities "have, and will continue to be conducted in compliance with Romania laws, EU requirements and stringent industry standards."

Shale gas drilling has fuelled a major controversy around the world, and the technique used, hydraulic fraction or fracking, has been banned in countries such as France and Bulgaria.

Environmentalists say the method poses serious threats to the environment from contaminating ground water to triggering earthquakes.

Romania's ruling centre-left coalition in power since May had slammed the previous - centre-right - government's decision to grant Chevron and other oil groups concessions to prospect for shale gas.

The government led by Prime minister Victor Ponta last year adopted a moratorium on drilling, putting Chevron's operations on hold.

But as the moratorium expired in December, Ponta recently said shale gas tapping should be approached in a "serious, positive way", adding he was in favour of exploration.

"People must carefully weigh the advantages and the disadvantages," said Buzatu, who last spring joined protesters telling Chevron to "go home" and "stop massacrating Romania."

He said: "For now it's only a question of knowing if Romania has such reserves or not."

Chevron, which was hoping to drill the first exploration well in the second half of 2012, plans to invest tens of millions of dollars if significant reserves are discovered.

A US Energy Information Administration study said the joint reserves for Romania, Bulgaria and Hungary were around 538 billion cubic metres, among the biggest in eastern Europe.