US oil group Chevron has announced plans to pull out of Polish shale gas exploration, commenting that exploiting the country's reserves there "no longer compares favorably" with other opportunities in its global portfolio.

The decision by Chevron, which had the largest commitment to Poland of all multinational companies, deals another serious blow to the east European country's hopes of becoming a major shale gas player.

As late as August 2014, Polish leaders said they expected commercial exploration to get off the ground in 2016. Prior to that, the start date had been seen as 2014.

Reasons for Chevron's pullback include downward revised estimates of the size of the reserves slumbering beneath Poland's soil as well as new assessment of the effort required to get the gas out of the ground.

Since 2012, a number of oil and gas giants, including Exxon Mobil, Total, Eni and Marathon Oil, initially lured by visions of originally massive exploitable reserves, have pulled out of the Polish market.

Along with the more difficult exploration prospects, the companies have also complained about a lack of transparency in government regulations. Contributing to the current unease is the steep fall in oil prices that has put paid to projects now seen as less solid, not only in Poland, but also in other countries.

In addition to Poland, Chevron also had drilled several exploratory wells in Romania and made commitments to Ukraine and Lithuania. Despite the current tensions, the US group still maintains an office in Ukraine, but all projects there are believed to be on ice.

Poland's initial embrace of shale gas exploration was seen to reflect efforts to become independent of Russian gas imports. In the meantime, the country has begun to tap new resources, among other things agreeing to import liquefied natural gas (LNG) from Qatar. It also is trying to improve its connections with the west European gas pipeline network.

Meanwhile, Chevron's wholly owned subsidiary, Chevron Mauritania Exploration Limited, has announced plans to acquire a 30% non-operating working interest in an offshore development project in Mauritania from Kosmos Energy. The deal is subject to Mauritanian government approves.

According to the Polish Geological Institute in Warsaw, the country's shale formations have proved difficult to drill. At best, it concedes, Poland is likely to have some isolated production areas rather than one big continuous shale belt originally touted by the government.