Oxygen permeation measurements on Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF), SrCo1-xNbxO3-delta (SCN; x=0.1, 0.2), Sr(Co0.8Fe0.2)(1-y)TiyO3-delta (SCFT; y=0.1, 0.2, 0.4), La2NiO4 (L2N), Ca0.5Sr0.5Fe0.2Mn0.8O3-delta (CSFM) and the dual phase material Ce0.8Sm0.2O1.9,+ Ag (CS + Ag) were carried out using CO2/N-2 mixtures as sweep gas. A breakdown of the O-2 permeation was observed for BSCF and SCN even at low CO2 concentrations. A protective layer of Ce0.8Gd0.2O1.9 on BSCF shifts the permeation breakdown to higher CO2 concentrations but was insufficient for pure CO2 sweep. SCFT samples show a stable O-2 permeation with CO2 sweep, but only at temperatures of at least 900 degrees C. The O-2 permeation for CO2 sweep drops down with time, especially at lower temperatures. The time dependency was fitted by a logarithmic regression to predict the total loss of the O-2 permeation. An excellent stability against CO2 was found only for L2N, CSFM and Cs +Ag. However, the O-2 permeation values amounted to less than one order of magnitude below BSCF. (C) 2011 Elsevier B.V. All rights reserved.