Caspian Sea
The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not a freshwater lake. It contains about 3.5 times more water, by volume, than all five of North America's Great Lakes combined. The Caspian was once part of the Tethys Ocean, but became landlocked about 5.5 million years ago due to plate tectonics. The Volga River (about 80% of the inflow) and the Ural River discharge into the Caspian Sea, but it has no natural outflow other than by evaporation. Thus the Caspian ecosystem is a closed basin, with its own sea level history that is independent of the eustatic level of the world's oceans.
Caspian Sea
The Caspian Sea region presently is a significant, but not major, supplier of crude oil to world markets, based upon estimates by BP Amoco and the U.S. Energy Information Administration, U.S. Department of Energy. The Caspian region produced an estimated 1.4–1.5 million barrels per day (bbls/day) including natural gas liquids in 2001, or 1.9% of total world output (table 1).3 More than a dozen non-Caspian countries each produce more than 1.5 million bbls/day. Caspian region production has been higher, but suffered during the collapse of the Soviet Union and the years following. Kazakhstan accounts for 55% and Azerbaijan for about 20% of current regional oil output.