A new technique was proposed to study the kinetics of high-temperature electrode reactions. A "porous" zirconia oxygen sensor (POS) was placed on a polarized working electrode, and the oxygen potential was detected on the surface. Its deviation from the gas phase gave information about the reaction between the gas phase and the adsorbed species. Several metal electrodes were examined in O2-Ar or H-2-H2O-Ar atmospheres, and the POS responses were compared. Evidence of a large contribution of the surface reaction to the electrode polarization was observed in some cases, e.g. oxygen reaction on a Pt paste electrode at low temperature, and hydrogen oxidation reaction on a Ni wire electrode. The potentiality of this method for the study of electrode kinetics and surface reactions is demonstrated.