CeO2 and CeO2/ZrO2 supports were prepared by two low temperature (500 degrees C) routes : calcination of hydroxide precipitates and firing mixtures of acetates. The supports were loaded with 0.5% Pt and characterized both fresh and aged (at 800 and 1000 degrees C). X-ray diffraction analyses show that a CeO2/ZrO2 solid solution is formed in the samples prepared by precipitation of the hydroxides and calcination at 500 degrees C. To our knowledge this is the lowest temperature chemical route (not including high energy ball milling) to CeO2/ZrO2 solid solutions yet reported. Samples prepared by firing the acetate mixtures had almost exclusively CeO2 and ZrO2 in separated phases. Oxygen storage measurements showed that the addition of zirconia increased the oxygen storage capacities (on a per gram of catalyst basis) over ceria alone for both preparation methods. In the phase separated materials the amount of reversibly stored oxygen was 1.7-2.5 times more per gram catalyst than that of ceria only. The beneficial effects of zirconia are most pronounced in the solid solutions which had oxygen storage 3-5 times higher than ceria. When the Zr concentration is optimized, the solid solution materials aged at 1000 degrees C showed higher oxygen storage than fresh CeO2. For both preparation methods, the optimal (per gram catalyst) Zr concentration was found to be 25 mol% Zr for samples aged at 1000 degrees C, however, the performance of the solid solution materials was somewhat insensitive to Zr loading between 15 and 50 mol% Zr.