The chemical stability of SrFeO3-based perovskites in H2O- and CO2-containing atmospheres at high temperatures and pressures has been examined. The extent of reaction as a function of pCO(2), pH(2)O, temperature, and time has been determined. Either strontium carbonate or Sr(OH)(2).H2O was observed on sample surfaces after exposure. Observation of two different reaction-rate behaviors could be explained by the formation of different products. The stability of the perovskite has been found to increase when the activity of Sr is decreased. Chemical stability in H2O/CO2 is important to understand in order to use these membrane materials for syngas production.