The effects of aging temperature and time on the oxygen storage capacity (OSC) of Pt-Rh-promoted Ce0.75Zr0.25O2 solid solutions were measured and correlated with the BET surface area and noble metal (NM) surface area in the catalysts. The NM surface area is better correlated with OSC than is with the BET surface area. On a practical level, our results demonstrated that, even when operating at 900°C with alternating oxidizing and reducing conditions, these materials deactivate slowly with a near t-1 time dependence. Deactivation rates for these catalysts are dependent on the NM loading with the highest loaded catalysts deactivating roughly half as fast as the lowest loaded catalysts. As the aging temperature is increased from 900°C to 1000°C, the deactivation rate becomes two to four2-4 times higher for all three properties (BET surface area, NM surface area and OSC). The lowest NM loaded samples are more sensitive to aging temperature than the highest loaded ones.