High-surface-area PrOy-ZrO2 mixed oxide, crystallized in the cubic fluorite structure, is synthesized for the first time as a single-phase material over a wide range of composition by sol-gel processing. X-ray powder diffraction shows that the material remains single phase even after thecal treatment In air to 900 degrees C. The oxygen storage capacity of PrOy-ZrO2, where praseodymium undergoes pr(3+) <-> Pr4+ interconversion, is assessed by temperature-programmed reduction with H-2. The results show that there is little oxygen storage capacity unless the PrOy concentration exceeds 25 mol %. A comparison of oxygen storage capacity from similarly prepared single-phase CeO2-ZrO2, PrOy-CeO2, and PrOy-CeO2-ZrO2 materials is presented. Measurements of lattice parameter and reducibility suggest that there are preferred associations that lead to PrOy-ZrO2 and CeO2-ZrO2 rather than PrOy-CeO2 in the ternary mixed oxide. An evaluation of model Pd catalysts, using PrOy-ZrO2 and CeO2-ZrO2 as support materials, in functional tests approximating warmed-up, steady-state operation of an automotive catalyst, is also reported.