A combined reactor and particle model was developed with which the effect of mass and heat transfer limitations inside the oxygen carrier particles on the axial concentration and temperature profiles in packed bed CLC could be correctly accounted for. It was concluded that during the oxidation cycle, the relevance of heat transfer limitations is negligible, but that resistances due to internal diffusion may play a significant role. This effect was found to be even stronger with the reduction cycles, where the effectiveness of the oxygen carrier particle was affected by higher activation energies and a low reaction order. With these models, more reliable predictions of the axial concentration and temperature profiles in packed bed CLC can be given, which are necessary to arrive at a proper design and a quantitative assessment of the suitability of packed bed CLC.