Russian oil major LUKoil announced reserves in Russia's sector of the Caspian Sea may compose total 33 billion barrels of oil equivalent.
LUKoil vice president Anatoly Novikov said the company had discovered five offshore fields in the sector of the Caspian Sea in recent years and planned to start producing by 2008.
LUKoil, which has the world's second biggest oil reserves among private oil majors after U.S. major ExxonMobil, has in the past delivered conflicting estimates of its Caspian fields.
The firm has said the majority of fields contained gas, which is very difficult to ship out from the land-locked sea due to limited market interest in neighboring states except Turkey.
Russia remains one of the few places in the world where oil majors can still book huge reserves, but investors usually focus on Siberia, rather than the Caspian Sea.
The Russian sector of the Caspian Sea is considered to be less explored than Azerbaijan's or Kazakhstan's because LUKoil only began working on it at the end of the 1990s.