A model incorporating crystallite-scale features of a catalyst is developed to predict the oxygen storage capacity (OSC) of a Pd-containing three-way catalyst. The model predicts the effect of Pd crystallite size, Pd-ceria interfacial contact, and Pd dispersion on the spillover and reverse-spillover of oxygen between Pd and ceria, and the resulting OSC with H-2 and CH4 as reductants. Consistent with the experimental findings, the model predicts that H-2 results in a higher OSC than CH4. The dependence of oxygen surface diffusivity on the temperature is used to predict the reported variation of OSC with temperature. The effective surface diffusivity with H-2 is estimated to be higher than that with CH4, which is attributed to the possible spillover of hydrogen in addition to the reverse spillover of oxygen. This work can be extended to gasoline applications and other transient catalytic systems where spillover and reverse spillover effects are significant.