The offer, which was sent to Rosneft last week, is for the development of the blocks at the offshore projects Sakhalin-3, Sakhalin-4 and Sakhalin-5.
Rosneft holds controlling stakes in Sakhalin-3's Veninsky block as well as in the Zapadno-Shmidtovskoye block at Sakhalin-4 and the Kaigansko-Vasyukanskoye and Vostochno-Shmidtovskoye blocks in Sakhalin-5.
Rosneft said a decision on the offer hasn't been made yet.