The retrieval of gas densities and aerosol extinction coefficients from satellite occultation measurements is usually handled in two steps: the separation of species (spectral inversion) and the separation of the spatial contributions of different atmospheric layers (spatial inversion). The reason for these sequential steps and their associated approximations is that a single-step inversion is computationally very demanding. In this paper we describe a global one-step method that can be applied to satellite data using reasonable computer resources.