Dudley's resignation, effective from December 1 of this year, follows a protracted struggle between the firm's British and Russian shareholders and was part of an agreement reached between BP and Alfa Access-Renova, the vehicle representing the four Russia-connected billionaires who own the other half of TNK-BP.

Chief operating officer Tim Summers will act as interim chief executive while the firm, which is Russia's third-largest oil company, decides Dudley's replacement at a December 11 board meeting.

The former head of the world's largest nickel mine Norilsk, Denis Morozov, has a solid chance of becoming the next chief executive, main shareholder Viktor Vekselberg has said.

BP-appointed Dudley leaves the firm as a founding CEO after five years. His resignation was the main component of a truce reached last summer between shareholders after a battle in which BP accused the Russian side of behaving like raiders.

In a December 1 e-mail to TNK-BP staff, Dudley warned of possible difficulties due to the new management.

"Now some very testing times lie ahead. The company is moving towards a new governance model and will soon have a new management team. There will be less reliance on BP experts and senior international leadership."

Just a handful of the 150 expatriates who worked in senior management and engineering positions in TNK-BP will remain at the oil producer by the start of next year.

Last week, TNK-BP sources said that Russian oligarchs have taken effective management control of TNK-BP, following the exodus of foreign executives from senior positions.

German Khan, a member of the quartet of Russia-connected tycoons and the firm's executive director, is seen as the main force to have made life tough for foreigners, sources have said, and the choice of Morozov as the likely candidate to succeed Dudley is viewed as coming from the oligarchs.