The oxygen nonstoichiometry of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF5582) was investigated by thermogravimetry resulting in values of 2.40 <(3 -delta)< 2.57 for the equilibrium oxygen content in the range 600 <= T/degrees C <= 900 and 1E-4 < pO(2)/bar < 0.4. The oxygen exchange kinetics was studied by electrical conductivity relaxation as a function of temperature in the range 550 <= T/degrees C <= 725 with chemical diffusion coefficients 1E-6 < D-chem/cm(2) s(-1) < 3E-5 and (k(chem)) = 64 +/- 12 kJ mol(-1). Self-diffusion and surface exchange coefficients, as well as ionic conductivities are estimated. (c) 2008 Elsevier B.V. All rights reserved.