WARSAW, Poland — Poland's recoverable shale gas reserves are far lower than originally forecast — between 346 billion and 768 billion cubic meters, according to a government estimate released Wednesday.

The report said that would be enough to fully satisfy Poland's gas requirements for about seven decades. But the figures are a disappointment for a country that had been hoping that its shale gas assets would last centuries and help it break its dependence on Russian gas imports.

A U.S. estimate last year put the reserves at some 5.3 trillion cubic meters, a figure that had fueled Polish ambitions for energy self-sufficiency.

Poland has huge stores of coal that generate 93 percent of the nation's electricity output, but it remains heavily dependent on Russian oil and gas for other energy needs. This dependence is expensive and a source of resentment in this former Soviet satellite state, which rejected Moscow-backed communist rule 23 years ago.

Currently, about 70 percent of Poland's annual needs of 14.4 billion cubic meters of gas are covered by Russian imports.

Deputy Environment Minister Piotr Wozniak stressed that the new shale gas estimates are preliminary and could be revised upward when findings are published from wells currently being drilled. The report says total reserves could be as high as 1.9 trillion cubic meters.

The estimates were released by the State Geological Institute and the Ministry of the Environment. Prepared along with the U.S. Geological Survey, the numbers are based on pre-1990 data taken from 39 wells drilled for research and exploration.

The United States is the only country so far to engage in widespread exploitation of shale gas, which is trapped deep below ground in porous rock. Several U.S. companies have licenses to drill in Poland.

Shale gas is located below ground across the European continent, from France to Ukraine, but many countries have decided not to attempt to extract it due to environmental concerns.