Velocity distributions of desorbing product CO2 were studied in the CO oxidation on Pt(557) over a wide range of surface temperatures, in both the active and inhibited regions at the steady state. The translational energy of CO2 in the active region, where the reaction is in a first order with respect to CO, is very high and it is insensitive to the surface temperature. It decreases sharply with increasing CO partial pressure in the boundary region. In the inhibited region, where the reaction is retarded by CO, the translational energy is relatively low and increases with increasing surface temperature. (C) 1999 Elsevier Science B.V. All rights reserved.