Abstract: A device and a method is disclosed for detecting an undesired escape of fluids, in that electric potentials are measured using a grid of non-polarizable measuring electrodes above an underground storage facility. Potential differences are determined in such a way that disturbances due to injection borehole or due to the exchange of fluids in the underground storage facility are eliminated. This is done either through the use of the symmetry of the potential distribution around the injection borehole in that the potential differences of pairs of measuring electrodes are observed whose mid-points coincide with the injection borehole or else through the computational simulation of the potentials that arise due to the fluid movement in the underground storage facility without a leak. These are then subtracted from the measured potentials. If the ascertained potential differences exceed a limit value, this is considered as an indication of a leak.