The electrochemical and chemical oxidation of the defect perovskite SrCoO 2.5 to the cubic perovskite SrCoO 3 at ambient temperature in alkaline electrolyte are shown to be reversible processes with the appearance of intermediate compounds; the phase diagram can be described by two line phases SrCoO 2.5 and SrCoO 2.75 and one solid solution range SrCoO 2.87+y with 0 < y < 0.13. The redox cycle displays a structural hysteresis under dynamic conditions. Several models are discussed in order to explain the unusual phenomenon of roomtemperature bulk oxygen transport.