DegassingDegassingof the EarthEarth is widelyGas Volcanism manifested in the World OceanWorld Ocean. In this Chapter, systematization of published data including those from the Black SeaBlack Sea, where degassing is especially well pronounced, is presented. Gas manifestationsGas manifestationsfrom the sea bottomsea bottom, including those from mud volcanoesmud volcanoes, are often referred to as cold seeps in contrast to deep thermal gas manifestations that are also known in the World Ocean. Cold degassing of the ocean floor is a global physical and geological phenomenon. Gas manifestations are found in all morphostructural zones from the shelfshelf to rift valleyssea bottomrift valleys of mid-ocean ridgessea bottomrift valleysmid-ocean ridges. In the Black Sea, they have been known since antiquity, but their scientific study started only in 1989. As a result of hydroacoustic observationshydroacoustic observations of the Black Sea bottom over the past thirty years, more than 5000 gas manifestations in the form of seepsseeps, flaresflares, torchestorches, and fountainsfountains have been discovered. In-depth study of their physical, hydrological, and chemical properties enabled us to identify them as cold methane seepagesmethane seepages. Over 25 years of monitoringGas manifestationsmonitoring, it was found that most of them retain stable characteristics in space and time.