U.S. energy major Chevron (CVX.N) has yet to complete an assessment of Romania's natural gas potential from shale, it said, one day after the country's prime minister expressed doubt about the existence of shale gas reserves there.

Prime Minister Victor Ponta, in the middle of a presidential campaign ahead of a Nov. 16 runoff which he is expected to win, said on Sunday that Romania had "fought very hard for something that we do not have." He did not elaborate.

Like its emerging European Union peer Poland, Romania has opened the door to firms seeking to discover shale gas, hoping to mirror a boom in cheap energy seen in the United States.

"Chevron is analysing the data gathered during its drilling and seismic operations to further understand the resource potential ofnatural gas from shale," Chevron told Reuters.

"When the analysis has been completed, the results will be provided to the National Agency of Mineral Resources (NAMR) and will remain in the (Romanian) state's custody."

Romania is the third most energy-independent EU member.

Earlier this year, Chevron said it finalised exploration works at a well in the eastern Romanian village of Pungesti, after repeatedly postponing operations because of protests from local residents.

Chevron also has rights for three licence blocks in Romania near the Black Sea, supporting a drive to find alternative gas resources which has become more urgent since the conflict broke out in Ukraine, through which Russia sends half of its gas exports to the EU.

The U.S. Energy Information Administration has estimated Romania could potentially hold 51 trillion cubic feet of shale gas, which would cover domestic demand for more than a century.