A vertical round container (1) for storing liquids comprises a floating cover (6) covering the surface of the liquid. The cover is sealed in relation to the container wall by means of flexible sealing elements (18, 19) and includes, on the lower side thereof, at least one compartment (62) which is open towards the liquid and contains gaseous media/vapors. Devices (40a) are provided for determining the submersion depth of the cover, and supply/discharge lines (29) are provided for modifying the quantity of the gaseous medium in the at least one compartment. The supply/discharge lines for the gaseous medium are connected to a central unit (28) provided outside the container region.