Cerium concentrate, a mixture of ceria (about 60 wt.%) and other rare-earth (mostly lanthanum) oxides, partially transforms into a solid solution upon high-energy mechanical milling. Temperature-pro rammed reduction of the milled material resembles that of the high-oxygen-storage material, ceria-zirconia, but the kinetics of oxygen removal, observed in pulse experiments with either CO or H-2, are much slower. The oxygen storage capacity of a Pd catalyst made with the milled material is found to be less than that of one made with unmilled material when measured on a short (<1 min) time scale.