Reaction rates for the water-gas-shift (WGS) reaction were measured on catalysts with 1-wt% Pd supported on CeO2, Ce0.5Pr0.5O2-x and PrO (x) in order to determine whether the weakly bound oxygen associated with Pr could enhance reaction rates. However, differential rates in 25 Torr of both CO and H2O showed that the activity of Pr-containing catalysts were much lower. Measurements of the oxygen content of these samples after reduction in dry H-2 at 873 K, after reoxidation in steam at 873 K, and following exposure of the catalysts to WGS conditions at 873 K demonstrate that ceria is easily reoxidized by steam and remains oxidized under WGS conditions, while the loosely bound oxygen associated with praseodymia or ceria-praseodymia is lost under WGS conditions and cannot be restored by oxidation in steam. These results can be understood by comparing the equilibrium redox properties of the support materials to the typical P(O-2) experienced under WGS conditions.