The relative importance of diffusion, reaction rates at the interfaces and ohmic losses is theoretically investigated for a porous perovskite cathode. Two models for the charge transfer mechanism at the cathode-electrolyte interface have been considered. The first model assumes direct passage of vacancies from the cathode to the electrolyte and predicts a sharp increase of the current density at high cathodic overpotentials. The second model assumes intermediate adsorbed oxygen atoms to be reduced at the cathode-electrolyte interface and predicts a limiting current behaviour in the cathodic direction. By qualitative comparison of the results with available experimental data, possible mechanisms for the cathode behavior at high overpotentials are evaluated.