A leakage warning system for containers, especially mineral oil product storage tanks, comprising a cover (5) which is sealed against the base (3) via at least one aperture (4) in the base (3) of the container (1) supported on a foundation (2) and convex in relation to the inside of the container, in which there is at least one spacer (12) in the region between the base (3) and the foundation (2) immediately adjacent to the aperture (4), and comprising a gas line (9) taken outwards from the cover (5) through the inside of the container and through the container wall and a gas measuring instrument (10) connected to its outer end.