US firm ConocoPhillips will halve its stake in the Russian oil major Lukoil within three years.
The drop from 20% to 10% would allow the US oil major to raise $4.6bn at current prices.
An anonymous source close to the deal said Conoco will announce the stake sale decision on March 24, Reuters reported.
The company has gradually built up its 20% stake since 2004.
Conoco has also invested in a joint production unit with Lukoil in Russia's Arctic, Naryanmarneftegaz.