The specific activity for benzene hydrogenation of nickel, cobalt, and platinum supported on silica is compared over the range of 70 ° to 175 °C at a common set of reactant partial pressures. The apparent activation energies were found to be 14.0, 5.8, and 2.3 kcal/mole for the nickel, cobalt, and platinum catalysts, respectively. The apparent activation energy increases with increasing hydrogen partial pressure. Below 90 °C the relative specific activity of the metals is Pt > Co > Ni. Because of the difference in apparent activation energies, above 90 °C the specific activity of nickel becomes greater than that of cobalt. Because of the complex nature of the apparent activation energy for benzene hydrogenation, the difficulty in quantitatively relating this parameter to the stability of proposed surface π complexes is pointed out.