Stationary polarization curves were obtained for porous lithium cobaltite cathodes under varying temperatures and oxidant compositions. The exchange current densities were determined from the slope at low overpotentials by means of numerical calculations, taking into account the current density distribution. Positive influences on the exchange current density were found both for the partial pressure of oxygen and carbon dioxide. The results are similar to earlier data obtained from measurements on NiO electrodes. The values are not consistent with either the peroxide mechanism or the superoxide mechanism, two mechanisms often proposed in the literature.