The auction involved several bidders, including Gaz de France. Fortum, which already owns a number of power generating assets in Russia, will pay for the stake within the next two to three weeks.
The Finnish company also said it would like to buy the state-owned territorial generating company's entire additional issue worth 46.6 billion rubles ($1.9 billion).
"If Fortum buys the additional issue, it will control at least 75% of TGK-10," Vladimir Avetisyan, an UES board member, said.
Andrei Shishkin, TGK-10 director general, said that his company had signed all the contracts with Russian energy giant Gazprom and independent gas suppliers for gas deliveries to its power plants. He said that the company's current capacity of 2,785MW could double by 2012.
Shishkin added that new power generating facilities currently being built with a maximum capacity of up to 2,700MW had been supplied with gas in full.
TGK-10 operates in West Siberia's Tyumen Region, the Khanty-Mansi and Yamal-Nenets autonomous areas, and the Chelyabinsk Region in the southern Urals.
