Four different pore diffusion models are fitted to iso-baric counter-diffusion fluxes measured in technical catalysts by a Wicke-Kallenbach cell over a 30-fold pressure range with different gas pairs. The models differ significantly with respect to predictive capabilities and computational requirements. Of the models studied, only the cross-linked pore model (Johnson and Stewart, 1965; Feng and Stewart, 1973), can predict diffusion fluxes reliably solely from pore size distribution. The study emphasizes the versatility and accuracy of the cross-linked pore model.