By means of impedance spectroscopic measurements, the electrode conductivity near the equilibrium potential was determined for the Pt,O-2/La0.88Sr0.12Ga0.82Mg0.18O2.85 electrode system as a function of the oxygen partial pressure (3-105 Pa) and temperature (816-1147 K). A model of two parallel processes proceeding in the electrode system is proposed. It is assumed that one of the reaction routes is localized at the platinum-gas interface and is limited by the diffusion of adsorbed oxygen on the platinum surface towards the three-phase "electrode-electrolyte-gas" boundary. The other route is localized at the "electrolyte-gas" interface and its rate is determined by the diffusion of electron holes in the electrolyte. The results of a calculation based on the proposed model are in accordance with the experimental data. The calculated values of the enthalpy and entropy of oxygen adsorption on platinum, the activation energy of oxygen diffusion along the platinum surface, and the activation energy of the hole transport in the electrolyte agree with literature data. (C) 2004 Elsevier Ltd. All rights reserved.