Very Fast Simulated Reannealing (VFSR) is applied to the solution of an inverse electromagnetic problem. The problem is to model the distribution of dipole current sources in a finitely resistive infinite half space. Modelling is done using the observed electrical potential on the inter-face between the half space and the free space. This method is known as Spontaneous Potential (SP) and is widely used for geophysical prospecting. Object of the VFSR algorithm is a quadratic error function between measured and synthetic data. Method is tested on a field data.