Oxygen permeation fluxes across the dense Ba0.5Sr0.5Co0.8Fe0.2O3-delta, (BSCFO) membrane disks were measured under an air/helium oxygen partial pressure gradient at high pressures (up to 10 atm) and various temperatures (973-1123 K). The fabricated BSCFO membrane exhibited good oxygen permeability with a high oxygen permeation flux of 2.01 ml min(-1)cm(-2) (thickness: 1.37 mm) at 1123 K and 10 atm. Oxygen permeation results were analyzed theoretically using the surface exchange current model. The dependences of the oxygen permeation fluxes on the oxygen partial pressure gradient, suggested that the bulk oxygen ionic diffusion was the rate-limiting step for the overall oxygen permeation process across the BSCFO membrane. The ambipolar diffusion coefficients (D-a), the oxygen vacancy diffusion coefficients (D-a) and the oxygen ionic conductivities (sigma(i)) of the BSCFO material at different temperatures (973-1123 K) were calculated. It was found that BSCFO possessed high oxygen diffusion coefficients and ionic conductivities, which resulted in the good oxygen permeability of BSCFO. In addition, the BSCFO membrane exhibited good stability of oxygen permeation at 1123 K, while the deterioration of oxygen permeation stability was observed at 1098 K due to structural changes occurring at the surface of the BSCFO membrane disk as demonstrated by XRD. (c) 2005 Elsevier B.V. All rights reserved.