WARSAW, Poland (AP) -- Poland's gas giant, PGNiG, and Chevron on Monday agreed to jointly hunt for shale gas in southwestern Poland in a move to speed up the exploration amid tension with major gas supplier, Russia.

Dependent on Russian imports, Poland wants to diversify its energy sources and is placing hopes in its reportedly sizable shale gas deposits. Warsaw is also urging the European Union to develop a joint energy system and decrease reliance on Russia.

European leaders are talking about possible economic sanctions against Moscow over its political conflict with Ukraine. Russia recently said it was raising gas prices for Ukraine, which also transits the fuel to central and western Europe.

"The experience of recent weeks shows that Europe must show more solidarity in the energy sector," Poland's Prime Minister Donald Tusk said over the weekend.

Tusk called for greater investment in Europe's gas network, on joint purchase policies and on a greater role in the energy mix for coal, which is Poland's top energy source, and shale gas, which is unpopular in Europe.

On Monday, PGNiG spokeswoman Dorota Gajewska said PGNiG and Chevron will jointly assess gas deposits in their areas of operation and will exchange geological information, which is vital for choosing exploration sites. Such information is scarce in Poland, due to the small number of exploratory wells. There are some 50 now, while hundreds are needed to offer a reliable assessment.

Chevron said in a statement that successful exploration could result in the "establishment of a joint company in which each holds a 50 percent interest."

The companies say cooperation will help cut costs and risks.

Chevron is currently assessing results from its four exploratory wells.

In Europe, only Poland and Britain are actively exploring for shale gas.