ConocoPhillips (COP) sold its indirect 30% interest in a Russian joint venture to co-owner Lukoil Holdings (LUKOY, LKOH.RS), part of the exploration and production company's effort to boost returns by divesting itself of billions of dollars in assets.

Financial terms weren't disclosed, but ConocoPhillips anticipates an after-tax gain of roughly $400 million from the sale of its stake in NaryanMarNefteGaz.

Speaking at the North America Prospect Expo in Houston Wednesday, Matt Fox, Conoco's executive vice president for exploration and production, said the company is winnowing its asset base to just those that will allow it to increase production and margins.

"If we have assets that can't contribute to that, they're gone," Mr. Fox said. "We're being pretty ruthless in the way we're trying to build the portfolio we want to get."

He said the company expects to sell $8 billion to $10 billion worth of assets in the next year or so.