The catalytic oxidation of propane on polycrystalline platinum films supported on yttria-stabilized zirconia was studied at 573-773 K and atmospheric total pressure. The technique of solid electrolyte potentiometry (SEP) was used to monitor the thermodynamic activity of oxygen adsorbed on the catalyst surface during reaction. Over a wide range of temperature and gas-phase composition, both the reaction rate and the surface oxygen activity were found to exhibit self-sustained isothermal oscillatory behavior. Reaction rate and oxygen activity oscillated simultaneously. Sustained oscillations were observed when the reactant ratio, PO2/P-C3H8, was kept between 1.2 and 2.2. At temperatures above 723 K, only stable steady states were obtained. The reaction kinetics and primarily the SEP data strongly indicate that the oscillatory phenomena are related to periodic formation and decomposition of a surface platinum oxide. (c) 2006 Elsevier Inc. All rights reserved.