Shortly after announcing plans to withdraw from shale gas exploration in Poland, US oil and energy group Chevron has said it will also pull out of Romania before the end of the year. With the latest move, it will bury its shale ambitions in Europe altogether.

Chevron said an assessment had shown that the Black Sea region does not compete favorably with other investment opportunities. Days earlier, it made similar remarks about Poland.

In 2012, the US group suspended its preliminary efforts to prepare for drilling in Romania amid mass public protests in the southeastern part of the country, where exploration was due to take place. In neighboring Bulgaria, hefty opposition to fracking led the government in 2012 to ban all activity.

"We understand the concerns in Romania. We believe that by presenting factual information on how these technologies are conducted, Romanians will understand that this natural gas is a clean source of energy and that it can be produced safely and responsibly," press reports at the time quoted Tom Holst, country manager for Chevron in Romania, as saying.

Chevron acquired rights for three license blocks in Romania near the Black Sea, and the US Energy Information Administration estimated that the east European country could potentially hold 51 trillion cubic feet of shale gas, covering domestic demand for more than a century.

By contrast, Romanian prime minister Victor Ponta in November 2014 said he believed the country did not have substantial reserves.

In addition to Poland and Romania, Chevron had also looked at Lithuania as well as Ukraine - before the current tensions there began.

Poland's initial enthusiastic support for fracking was seen to reflect efforts to become independent of Russian gas imports. In the meantime, reports say the country has begun to tap new resources, among other things agreeing to import liquefied natural gas (LNG) from Qatar.