The Caspian Sea, a particular sea that has become one of the most important hydrocarbon producing regions after the Persian Gulf

The Caspian Sea is an  of brackish water (salinity: 12.5 / thousand) without exit to the sea (endorheic) located between Europe and Asia. Its surface is 371,000 km (the largest lake in the world) and its maximum depth of almost 100 meters. It is 1210 km long and about 250-430 km wide. Its coast is 28 meters below sea level.
It is fed by the Volga, Ural, Emba and Kurá rivers. Due to its prolonged isolation from the rest of the seas (it was isolated geologically some 5.5 million years ago) its ecosystems evolved independently and there are species with their own characteristics that are not found in open seas. An example is the sturgeon that is fished for the production of caviar (lately it has suffered heavy overfishing) and the Caspian seal, which is the only seal that lives in fresh water (a related species is also found in Lake Baikal, which just as the Caspian is also an endorheic body of water).

The oil and gas region of the Caspian Sea, which includes Russia, Azerbaijan, Kazakhstan, Turkmenistan and Uzbekistan, is one of the oldest hydrocarbon production areas in the world playing an increasingly important role in world production.
The area has important reserves both offshore and in the emergent areas of the basin. At the same time, its importance as a producer of natural gas is increasing rapidly.
It is estimated that there are some 48,000 million barrels of oil and 292 trillion (292,000,000,000,000) of natural gas in the sedimentary basins of the Caspian Sea and surrounding areas. The offshore fields represent 41% of the crude oil and 36% of the natural gas of the entire Caspian basin.
Most of the offshore reserves are in the northern sector of the Caspian Sea, while natural gas reserves are in the southern region. According to U: S estimate. Geological Survey would have about 20,000 million of oil and 243 billion of natural gas that have not yet been discovered. Most of the latter are in the south where disputes over water rights make exploration difficult.
It can be estimated that the Caspian region produces an average of 2.6 million barrels per day, which is 3.4% of world production.
In the recent decade, the continental fields of Kazakhstan were those that contributed mainly to regional production, particularly the Tengiz field. During the 2006-2008 period, Azarbaiján developed the offshore Azeri-Chirag-Guneshli fields, significantly increasing its offshore production share. There is also oil production in Turkmenistan near the coast and in the Russian region north of the basin.