Rosneft said it paid $28 billion for the 50 percent stake in TNK-BP held by AAR, a group representing Russian interests in the Anglo-Russian venture.
"Agreements reached today enable us to start preparing the integration process immediately," Rosneft President Igor Sechin said in a statement.
Rosneft this year reached a deal with BP to buy its half of TNK-BP for more than $17 billion in cash.
This week the Russian Federal Subsoil Agency announced TNK-BP subsidiary Samotlorneftegaz submitted the largest bid for the Lodochnoye field in eastern Siberia. The field is said to hold recoverable reserves of around 315 million barrels of oil and roughly 2.4 trillion cubic feet of natural gas, reports Russia's state-run news agency RIA Novsoti.
RIA Novosti describes TNK-BP's latest acquisition as a potential win for Rosneft. Its Vankor field is near Lodochnoye and is exporting oil currently through the East Siberia-Pacific Ocean Pipeline to China.