Abstract: A buoyant marine storage vessel for fluids, such as oil, includes a flexible containment bag having at least a controllable inlet and outlet for fluids and a wire rope cage for the bag which is attached to the bag in such a manner that emptying of the fluid content of the bag is enabled by the buoyant pressure of water in which the vessel is located. The vessel can be anchored at a desired location and may include a buoyant support and protective frame having sections articulated on two perpendicular axes. Clusters of vessels may be created for storing large volumes of fluid with economy.