Controversy among the five littoral states over the legal regime of the Caspian Sea began with the breakup of the Soviet Union in 1991. Until that time, the Caspian was considered a “common Sea” between Iran and the Soviet Union. However, following the collapse of the Soviet Union, the number of littoral states increased from two to five, which in turn altered the geopolitical situation of the Sea. The birth of the new nation-states on the coast of the Sea transformed the region into a conflict area and the legal regime of the Sea became one of the contentious disputes among the bordering countries. The existence of offshore hydrocarbon resources in the Caspian and its location on a geopolitically significant transport route turned it into one of the main priority issues in the foreign policies of the littoral states and increased the need to find a legal solution, the absence of which prevented the disputing states from investigating the vast natural resources of the Sea. Therefore, since 1990, all five coastal states of the Sea have been more or less involved in the dispute over the ownership of the oil fields. The most adamant dispute has been between Azerbaijan and Turkmenistan.