To optimize geological structures a multi-physics inversion of electromagnetic and gravity data is carried out. With the TERRASYS’ Joint Inversion Framework JIF and its modules for 3D EM (here CSEM) and for 3D GRAV (gravity and gradients) the geometry of a salt body located in the Nordkapp Basin is optimized. The physical effects of a complex structural model, derived from seismic interpretations, are fitted to the field data by optimizing salt shape and rock parameter distributions simultaneously. Exemplary model features of the optimized models illustrate the improved solution space of the joint inversion compared to the respective per-datatype inversions. By means of this case study, benefits, preconditions and limits of joint inversion were discussed, as well as general quality criteria to evaluate achieved multi-data and multi-physics model optimizations.