For CO adsorption on PdAg/Ag(111) surface alloys with very low Pd contents, prepared by deposition at room temperature, Muir et al. reported a CO desorption peak at 279 K, which they attributed to CO desorption from Pd1 monomers . At a higher Pd coverage, a second desorption peak appeared at 370 -390 K, assigned to CO desorption from Pd2 bridge sites. These desorption temperatures are rather close to the peaks at 316 K and 364 -380 K reported for CO desorption from on top adsorption on Pd1 monomers and bridge bonded CO on Pd2 dimers in PdAg/Pd surface alloys . Hence, the additional strain effects and vertical ligand effects introduced when changing from Pd1 monomers and Pd2 dimers in a PdAg surface layer on Pd to Ag result only in a rather small increase in CO adsorption energy for adsorption on Pd2 site, while for adsorption on Pd1 monomers it is more pronounced. Calculations for CO adsorption on PdAg/Ag/Pd had shown that the presence of one or two Ag underlayers on Pd underneath the PdAg surface layer leads to a decrease of the CO adsorption energy [114], while the larger lattice constant of Ag should lead to an increase. Hence, these effects will at least partly compensate each other, which explains at least qualitatively the little difference in CO binding energy on Pd1 monomers and Pd2 dimers in these two systems.