Oxygen permeation measurements were performed on dense symmetric samples of Ca0.5Sr0.5Ti0.6Fe0.15Mn0.25O3-delta and compared to CaTi0.6Fe0.15Mn0.25O3-delta in order to assess the influence of the perovskite lattice volume on oxygen permeation. Oxygen flux measurements were performed in the temperature range 700-1000 degrees C and as function of feed side pO(2) from 10(-2) to 1 bar, and at high pressures up to 4 bar with a pO(2) of 3.36 bar. The O-2 permeability of the Sr-doped sample was significantly lower than that of the Sr-free sample, amounting to 3.9 x 10(-3) mL min(-1) cm(-1) at 900 degrees C for a feed side pO(2) of 0.21 bar. The O-2 permeability of CaTi0.6Fe0.15Mn0.25O3-delta shows little variation with increased feed side pressures and reaches 1.5 x 10(-2) mL min(-1) cm(-1) at 900 degrees C for a feed side pO(2) of 3.36 bar. This is approximately 1.5 times higher than the O-2 permeability with a feed side pO(2) of 0.21 bar. Furthermore, in order to assess the applicability of CaTi0.6Fe0.15Mn0.25O3-delta as an oxygen membrane material, creep tests were performed under compressive loads of 30 and 63 MPa, respectively, in air in the temperature range 700-1000 degrees C; the results indicate a high creep resistance for this class of materials. The measured O-2 permeabilities and creep rates are compared with other state-of-the-art membrane materials and their performance for relevant applications is discussed in terms of chemical and mechanical stability. (C) 2015 Elsevier B.V. All rights reserved.