Solid solutions of CeO2 with Yb2O3, Y2O3, Sm2O3, Gd2O3, La2O3, Nb2O5, Ta2O5, and Pr6O11 were prepared by sol-gel methods. All of the samples exhibited a single, cubic phase in x-ray diffraction and the lattice parameters were consistent with formation of the solid solutions. Surprisingly, all of the mixed oxides exhibited a much lower catalytic activity for n-butane oxidation than that of pure CeO2 at 650 K, with Sm0.2Ce0.8O1.9, Gd0.2Ce0.8O1.9, La0.2Ce0.8O1.9, Nb0.1Ce0.9O2.05, and Ta0.1Ce0.9O2.05 showing rates less than 10-2 that of pure ceria. Lower dopant levels with Sm+3 and Gd+3 affected the rates proportionately less. The implications of these results for use of ceria as an oxidation catalyst are discussed.