US oil giant Chevron obtained permits to explore for shale gas on Romania's Black Sea coast, the Environment Ministry said Wednesday, despite controversy about risks of the technique known as fracking.

"The environment protection agency of Constanta county, in south-eastern Romania, has delivered seismic prospecting permits for the Costinesti and Vama Veche blocs," the ministry told AFP.

The permits will allow Chevron to conduct "controlled explosions" at depths of between 10 and 15 metres (32 to 49 feet) within an area that measures 1,800 square kilometres (695 square miles).

In January, the company had been granted zoning certificates in the eastern Romanian region of Barlad, a boost to its local operations.

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

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

Environmentalists say the method poses serious threats that include contaminating ground water and triggering earthquakes.

Chevron maintains that all its activities "have, and will continue to be conducted in compliance with Romanian laws, EU requirements and stringent industry standards."

Romania's ruling centre-left coalition, in power since May 2012, had slammed the previous 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 after the moratorium expired in December, Ponta said he was in favour of exploration.

Environment minister Rovana Plumb last month said that shale gas exploration "posed no risk", and added that Romania should find out if it really had significant reserves.

A US Energy Information Administration study said the joint reserves for Romania, Bulgaria and Hungary were around 538 billion cubic metres (19 trillion cubic feet), among the biggest in eastern Europe.