The reaction rate and the ethylene/ethane product ratio in CO hydrogenation increase when cobalt wire, used as a catalyst for the reaction, is reduced to lower extents. The kinetic results obtained with the poorly reduced wire correlate well with temperature-programmed surface reaction(TPSR) and H chernisorption results, and are interpreted to be due to electronic modification of the cobalt surface by the unreduced subsurface cobalt oxide. It has been concluded that the extent of metal reduction is an important variable in determining the catalytic property of cobalt.