past and ongoing oil and gas reservoirs) should cause the CO 2 to form hydrates and hence act as a long term depository of excess CO 2 . The Sleipner gas field, a natural gas field in the North Sea, is already used as facility for carbon capture and storage (CCS) and is the world's first offshore CCS plant, operative since October 1996. Sleipner has stored about one million tonnes of CO 2 a year at a depth of 800 -- 1000 m below the seafloor. There has been no evidence of leakage so far and multinational and multidisciplinary research projects are underway to assess the CO 2 state, to investigate any potential impacts and to predict the long-term destiny of the CO 2 [120] , [121] . This existing operation, and another in the Snohvit gas field in the Barents Sea that stores 700,000 tonnes CO 2 per year at depths of 320 m, are relatively small-scale when compared with proposed industrial scale CO 2 disposal, which would store about 1000 times this amount. A simpler and cheaper option that has been considered is the direct disposal of liquid CO 2 onto the deep seabed, based on the principle that a gas hydrate will be generated on the seabed. Preliminary experiments have shown that surface disposal is feasible. However, small-scale experiments have shown that fish swimming into the CO 2 plume are narcotised, although they recover as they drift out of the CO 2 cloud [122] . Scavenging fish