Binary oxide spinels composed of Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, and Zn were synthesized. Electrical conductivity was measured in air at 500 degrees-800 degrees C. Thermal expansion was measured from room temperature to 1000 degrees C. Ferrite spinels have thermal expansion coefficients of 11-12 ppm/K, compared with 7-9 ppm/K for other spinels except Cu-Mn and Co-Mn which show anomalous behavior. The highest electrical conductivity among transition metal spinels was found for MnCo2O4 (60 S/cm at 800 degrees C) and Cu1.3Mn1.7O4 (225 S/cm at 750 degrees C).