To reduce the CO2 emissions of fossil fuel fired power plants by separating CO2 out of the process is one important step to migitate the greenhouse effect. One discussed process is to concentrate carbon dioxide in the power plant process by coal combustion using oxygen instead of air. If the required air separation is realised by a MIEC membrane, it will be possible to reduce the efficiency drop of the power plant. For development of membrane moduls for industrial applications it is necessary to study membrane materials under comparable conditions to the power plant. To reach high enough O2-permeation rates membranes have to be as thin as possible and they have to be mechanically and chemically stable under the operating conditions (T > 800°C, ΔP = 20 bar). Furthermore the MIEC membrane has to withstand all contacting materials and gases without decomposition of the membrane material. Therefore experimental studies are made under various thermal, mechanical and chemical conditions. Main topic is to test the influence of flue gas components CO2, SO2, CO, NO and water each of variable concentrations on the permeation rate, the membrane long time stability and the changings of the material microstructure. The influence of flue gas components on perovskite and non-perovskite types Ba0,5Sr0,5Co0,8Fe0,2O3-dBSCF), Sr0,5 Ca0,5 Mn0,8 Fe0,2 O3-d (SCMF) and La2NiO4-d has been studied with the result that some types have been shown higher chemical stability combined with much lower permeation rate. In addition the permeation rate as a function of membrane thickness and O2-partial and absolut pressure has been investigated. The permeate pressure has been varied from 40 mbar to 1 bar combined with high feed pressures up to 20 bar at the same time. Permeation rates about 10 mlN/cm2min at temperatures about 900°C have been measured. These experimental results combined with a CFD-based simulation of the experiments provide a basis to fit the materials constants of the wagner-equation and to estimate limitations by surface kinetics.