Many of the reactions for hydrocarbon reforming, including steam reforming and water-gas shift, can be thought of as redox reactions. It is therefore not surprising that catalytic activities can be enhanced significantly by including a redox catalyst, such as ceria. In most cases, the redox catalysts are in the form of a mixed oxide, such as ceria-zirconia, and the thermodynamic properties for oxidation and reduction of these mixed oxides are usually not known. In this talk, I will discuss our investigations into the redox properties of selected materials, including solid solutions of ceria and zirconia. Reduction isotherms were determined over a temperature range using TPR methods and Coulomb Titration. For ceria-zirconia, the thermodynamic properties were found to be a strong function of composition but were independent of sample surface area and calcination temperature, so long as the oxide structure was maintained. While the enthalpy of reduction for ceria-zirconia solutions is less than that of pure ceria, at least some of the interesting properties of this material are associated with entropy effects.