The electrical transport properties of SrFeCo 0 . 5 O x were studied in various oxygen partial pressure (p o 2 ) environments by conductivity experiments. Oxygen stoichiometry was determined by thermogravimetric analysis, while oxygen chemical diffusion coefficient was derived from time relaxation experiments by abruptly changing the p o 2 in the surrounding atmosphere and monitoring specimen weight change as a function of time. The structure of SrFeCo 0 . 5 O x was determined by X-ray powder diffraction. Conductivity results showed that SrFeCo 0 . 5 O x is a mixed conductor with high combined electronic and oxygen ionic conductivities. At 950°C in air, total electrical conductivity is 23 S cm - 1 and the ionic transference number is 0.4. In high-p o 2 environments, interstitial oxide ions and holes are the predominant charge carriers in SrFeCo 0 . 5 O x . We found that oxygen transport in SrFeCo 0 . 5 O x is primarily bulk controlled, and X-ray diffraction revealed that the SrFeCo 0 . 5 O x system has an oxygen-deficient perovskite-like layered structure. Its structure can be fit by Rietveld analysis with an orthorhombic unit cell of lattice parameters a = 11.112, b = 19.12, c = 5.528 9, and cell volume of 1174.67 9 3 .