The structure and oxygen stoichiometry of Ba0.5Sr0.5Co0.5Fe0.5O3-delta (BSCF) between 793 K and 1100 K at an oxygen partial pressure of 0.1 atm were determined by in-situ neutron diffraction. Additional analysis at room temperature was conducted by synchrotron X-ray diffraction. BSCF has the cubic perovskite structure, space group Pm (3) over barn, for all investigated temperatures. The oxygen stoichiometry ranged from 226 (2) at 1100 K to 2.36 (2) at 793 K. The formation of secondary phases during long equilibration periods is suggested to be responsible for the discrepancy between oxygen stoichiometry values determined by neutron diffraction and those determined by thermogravimetry for this class of materials. (C) 2013 Elsevier B.V. All rights reserved.