Mixed electron hole and oxide ion conducting perovskite-type oxides. La0.8Sr0.2(Ga0.8Mg0.2)(1-x)CrxO3-delta (0 <= x <= 1.0). were prepared by solid state reaction. The phase stability and the oxygen permeation properties of the oxides were examined as a function of the content of Cr. La0.8Sr0.2(Ga0.8Mg0.2)(1-x)CrxO3-delta has a perovskite related tetragonal phase with x=0.1 to 0.8. The total electrical conductivity of La0.8Sr0.2 (Ga0.8Mg0.2)(1-x)CrxO3-delta increases with increasing x. The oxygen permeation flux across the La0.8Sr0.2 (Ga0.8Mg0.2)(1-x)CrxO3-delta membranes at higher temperatures increases with x up to x = 04. The maximum oxygen permeation flux of 1.6 x 10(-7) mol(-1) cm(-2) at 1100 degrees C in a oxygen activity gradient of air/10(-2) Pa is observed in La0.8Sr0.2(Ga0.8Mg0.2)(0.6)Cr0.4O3-delta. This perovskite-type oxide is stable under an oxygen partial pressure of 7 x 10(-10) Pa at 1000 degrees C. (c) 2009 Elsevier B.V. All rights reserved.