Japanese trading house Mitsui & Co. Ltd. (8031.TO) Thursday became the first Japanese company to enter into a European shale gas project by agreeing to acquire a 9% stake in Polish exploration concessions from subsidiaries of Marathon Oil Corp. (MRO).

Financial terms weren't disclosed.

"
Poland is considered to be one of the most attractive shale gas potential areas in Europe , where the development of shale gas by the major oil and gas companies is expected to accelerate," Mitsui said.

Poland could have 5.3 trillion cubic meters of shale gas, equal to more than 300 years of the country's annual gas consumption, according to the U.S. Department of Energy. If it turns out to be economically viable to extract, shale gas would reduce Poland 's natural gas supply dependence on Russia 's OAO Gazprom (GAZP.RS).

The 10 concessions, encompassing 2.1 million acres (850,000 hectares), are located in a band spanning from north
Poland to its eastern border, according to a map enclosed in Mitsui's statement.

In a separate statement,
Marathon said it will hold a 51% working interest in these 10 concessions and serve as operator. Nexen Inc. (NXY), another partner, owns a 40% working interest in the concessions. The closing of the transaction is contingent on approval by Polish government authorities and Nexen, Mitsui said.

"Seismic and other geological analysis, as well as drilling of exploration wells to evaluate technical potential of the concessions will be carried out over the next five years," Mitsui said.

Marathon said its agreement with Mitsui "provides further financial risk mitigation and aligns the company with another strong partner as Marathon , Mitsui and Nexen prepare to explore and evaluate the full potential of these concessions."

Mitsui said it is also conducting shale gas development and production activities in the Marcellus Shale, in
Pennsylvania , and said with the "experience and knowledge acquired from this project, we intend to expand our presence in the European gas market, which follows the U.S. gas market."