Oxygen reduction on two well-defined iron oxide electrodes (gamma-FeOOH and Fe3O4) shows deviations from linear Koutecky-Levich plots. These results can be explained by two limiting cases of the heterogeneous catalytic peroxide decomposition mechanism proposed by McIntyre (J. Phys. Chem., 71 (1967) 1196; J. Phys. Chem., 73 (1969) 4102). Recycling of oxygen by peroxide decomposition at the oxide surfaces depends on the relative magnitude of the peroxide decomposition rate (k(4)), the convective-diffusion flux (Z(p)W(1/2)) and the oxygen adsorption kinetics (k(2)/k(-2)).