In the potential range of the peak A1 and below in the negative-going scan, increasing the UPL results in a shift of the steep decline in COOR current to lower potentials, both for the Pt-1 and the Pt-3 electrode. Since the steep increase of the COOR current in the positivegoing scan does not shift significantly, the hysteresis becomes broader with increasing UPLs. Starting with the Pt-3 electrode, the shift of the steeply declining COOR current to lower potentials with increasing UPL must be due to an increasing amount of OH/O species on the surface, which lowers the COOR rate at potentials positive of 1.0 V. These species can support the COOR for a longer time and thus to lower potential in the scan. Once most of these species are consumed reactively, rapid blocking of the surface by adsorbed CO sets in. This explanation closely agrees with previous modelling results for CO bulk oxidation on Pt, where such shifts had been related to the larger degree of OH/O formation on the sample at high potentials. For the Pt-1 electrode, where the COOR current in the potential range of the peak A1 does not seem to vary with the UPL, the explanation must be more complex. Clearly, one would expect a similar physical reason for the observed down-shift in the COOR current decline for potentials more negative than peak A1 as for the Pt-3 electrode. But in the case of the Pt-1 elec-trode, restructuring effects must also be considered, which may further affect the COOR rate at potentials lower than peak A1.