The perovskite Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3-d (BSCF 5582) has attracted great interest as an oxygen reduction catalyst for solid oxide fuel cells and as an oxygen permeation membrane material. Mixed ionic and electronic conductivity is essential to the high catalytic activity it exhibits, however its electronic behavior and overall defect chemistry are not well understood. The related material SrCo 0.9Nb 0.1O 3-d (SCN 091) is another promising composition that may have comparable performance, but with defect chemistry that is simpler to study. From a combination of thermogravimetric, impedance, and diffraction measurements we find SCN 091 to exhibit somewhat smaller oxygen nonstoichiometry, five times higher electronic conductivity, lower enthalpy of hole migration, and greater structural stability than BSCF 5582. We also observe that the enthalpy of hole migration in such materials tends to increase as oxygen content decreases; the origins of this behavior are unclear.