Lukoil said the acquisition gives it control over joint venture Naryanmarneftegaz, which operates in Timan Pechora province in northern Russia.
"In view of the sale of ConocoPhillips' 30 percent interest in NMNG as part of its divesture program for 2012, LUKOIL is aiming to strengthen and consolidate positions in its key upstream region -- Timan Pechora oil and gas province," the Russian company said in a statement.
The financial terms of the transaction weren't disclosed. The U.S. company, however, said it expected to get an after-tax benefit of around $400 million from the divestment.
Conoco described the sale as part of a strategy to reposition its asset base.
"The sale of this non-core quality asset is an important component of our divestiture program for 2012," said Don Wallette, executive vice president for business development, at Conoco in a statement. "We are pleased that Lukoil, the co-owner of NMNG, recognizes the value of this asset."