Oxide compositions in the system Sr-Co-O were prepared by solid-state reaction. The oxide-oxygen reactions were investigated by thermo-gravimetric measurements. Equilibration was controlled by an amperometric lambda sensor. Thermodynamic data for the oxide-oxygen reaction were calculated. For the reaction CoO/Co3O4 With complete change of crystal structure between ferrite-and NaCl-types, the amount of oxygen exchanged (delta=1), and the absolute values of changes in enthalpy and entropy are the highest. The lowest values were observed for the partial molar enthalpy of the solid-solution reaction of oxygen with the stable perovskite phase Of Sr0.965Ce0.035CoO2.535+n. (c) 2006 Elsevier B.V. All rights reserved.