MIEC membranes (mixed ion-electron conducting membranes) are attracting increasing interest for industrial applications in which oxygen-enriched air or pure oxygen is used. One of these applications is the oxyfuel power plant process. High oxygen permeability and adequate chemical stability under operating conditions, especially with respect to CO(2) and SO(2), are therefore essential. In the work described here, permeation and chemical stability tests were performed with tubular membranes made of Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-delta) (BSCF), Sr(0.5)Ca(0.5)Mn(0.8)Fe(0.2)O(3-delta) (SCMF) and La(2)NiO(4+delta). To investigate the effects on the materials, microstructure analysis were performed before and after each experimental run by means of energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the highest permeability can be reached with BSCF membranes, but BSCF displays instability with respect to CO(2). The other materials show higher chemical stability without any significant degradation effects caused by CO(2), but they do display instability if the sweep gas contains 360 ppm SO(2). Furthermore, poisoning of the membrane materials by chromium evaporated from the steel was detected in the case of BSCF and SCMF membranes. (C) 2010 Elsevier B.V. All rights reserved.