The mixed ion-electron conductor Ba0.5Sr0.5Co0.8Fe0.2O3-delta has a strong application potential as high-temperature gas separation membrane. However, for real components the mechanical integrity of this brittle perovskite ceramic will be challenged by the boundary conditions of transient and stationary temperature exposure. In particular, long-term failure mechanisms such as static fatigue at room temperature and creep rupture at operation temperature may occur. The relevance of both effects is assessed. The effect of slow crack growth at room temperature has been investigated using fracture stresses obtained in biaxial bending under different loading rates. The provided data permit to assess the fracture stresses for different loading rates. Furthermore, a strength-probability-time plot is derived that permits a prediction of the lifetime under static loading conditions and hence the long-term reliability at room temperature. The creep rupture at typical operating temperatures was analysed using three-point bending tests permitting a determination of the failure stress in this application-related combined tensile-compressive mode. The creep rupture data are described by a modified Monkman-Grant relationship. (C) 2011 Elsevier B. V. All rights reserved.