To clarify the possibilities of existence of hydrocarbon gas hydrates in the sedimentary rocks of the Caspian Sea, the results of numerous investigations of their properties, conditions of their formation and effect on the physical properties of the sediments containing them have been considered. It is concluded that the region of possible hydrate formation in the Middle Caspian is limited by the isobath -390 m, and in the Southern Caspian -480 m. The thicknesses of the zones attain 134 and 152 m respectively. Recommendations are given on the prospecting methods which include the use of geoacoustic profiling.