"We believe the bankruptcy process was seriously flawed. BP Amoco will be carefully reviewing its business position in Russia in the light of this sale," Howard Chase, director of external affairs for BP Amoco Russia, said.

Tyumen Oil Company, known by its Russian initials TNK, bought Chernogorneft at a bankruptcy auction in Nizhnevartovsk, Siberia, for around $176 million, and said in a statement that it was determined to help BP Amoco and other investors stay in Russia. Several of Chernogorneft's other creditors, who include the European Bank for Reconstruction and Development and the Soros Foundation, have complained about the way in which the bankruptcy process and sale were conducted.

The handling of the bankruptcy of Sidanko and its subsidiaries is regarded as a key test of Russia's ability to attractand keep foreign investment, with many potential investors monitoring BP Amoco's fortunes closely.