"The commission's investigation confirmed that the proposed acquisition did not raise competition concerns because the merged entity would continue to face constraints from a number of strong competitors, while its customers would be capable of switching both to other suppliers as well as to other means of transportation for their crude oil demands," it said.
Rosneft last year agreed to acquire energy giant TNK-BP in deals with British energy company BP and AAR, a group representing the interests of four Russian billionaires in the consortium.
Rosneft said it paid $28 billion for the 50 percent stake in TNK-BP held by AAR. This year, the state-owned oil company reached a deal with BP to buy its half of TNK-BP for more than $17 billion in cash.
The European Commission said it left issues over Rosneft's ownership open because it didn't raise any competition concerns.
"The commission therefore concluded that the transaction would not significantly impede effective competition in the European Economic Area or any substantial part of it," it said.