The move is the latest blow for Polish hopes to find massive shale gas reserves that would help ease the country's dependence on Russian energy sources.

An ExxonMobil statement made available Monday to The Associated Press said it was ending its search because "there have been no demonstrated sustained commercial hydrocarbon flow rates."

The company said nothing about the future of the six licenses it has in Poland.

Economy Minister Waldemar Pawlak said he received the decision "with understanding," because ExxonMobil has "big interests being pursued in Russia."

He said the US company should either give up its licenses, or sell them to another firm. ExxonMobil acquired six licenses in central and eastern Poland in 2009 and 2010, on the spur of great success companies had in shale gas exploration in the US, in comparable geological conditions.

Pawlak noted that other major companies continue their exploration for unconventional gas, including another US firm, Chevron, and Poland's gas and oil giant, PGNiG.

Some two-dozen global energy companies are searching for shale gas across Poland. The country's energy hopes were also hit this year when a geological study estimated recoverable reserves at no more than some 768 billion cubic meters, much less than originally hoped.