The rate of CO oxidation by NO2 over Pd(100) was measured at CO and NO2 partial pressures of 1 and 0.05 Torr, respectively, and temperatures in the range 385-415 K. These results explain the non-Arrhenius behavior previously reported for the CO2 formation rate in the CO + O-2 + NO reaction over Pd(100) and show that the difference between Pd and Rh is even more dramatic for the CO + NO2 + NO reaction than for the CO + O-2 + NO reaction.