The structure, formation and stability of PtAg/Pt(111) surface alloys had been characterized previously by a variety of different techniques, the results were summarized previously by Jankowski et al. and by Bauer et al. These studies found that deposition of submonolayer amounts of Ag on Pt (111) and subsequent annealing to about 620 K results in the formation of monolayer PtAg surface alloys, where the Ag atoms are confined to the topmost layer with a tendency to phase separation to form two-dimensional, homoatomic ensembles rather than a random distribution. Thermal and CO induced intermixing of Pt and Ag in Ag films on Pt(111) and in Pt film covered Ag(111) surfaces were investigated by Jankowski et al. experimentally and by Hua et al. theoretically. Most important for the present study is the finding of a pronounced ligand effect, with neighboring Ag surface atoms, leading to a strengthening of the Pt-CO bond, due to an increased back-donation from the Pt atom into the 2* orbital of the adsorbed CO. Counteracting effects resulting from the compressive strain, due to the larger size of the Ag atoms and the pseudomorphic growth of the surface alloy, seemed to be less important. These experimental results, which were based mainly on temperature-programmed desorption (TPD) and infrared spectroscopy (FTIR) results, were supported also by DFT calculations. Furthermore, the authors reported distinct changes in the adsorption site on these surface alloys with increasing COad coverage, which also depended on the Ag surface concentration and thus on the relative concentration of small ensembles such as Pt1 monomers, Pt2 dimers, compact Pt3 trimers and larger Pt ensembles. A later high-resolution XPS study, which could distinguish also bridge-bonded CO from on-top adsorbed CO based on their slightly different C1s binding energies, essentially confirmed these findings. In the present study, we are particularly interested in identifying possible highly stable local structures and in correlations between electronic properties of specific Ptn ensembles and their CO adsorption strength. Considering the CO adsorption behavior we are most interested in changes in the adsorption characteristics with increasing local coverage, i.e., with increasing number of COad per Pt surface atoms in Ptn ensembles in bimetallic surfaces. This expands on our earlier report, where we had explored the low-coverage CO adsorption behavior on small Ptn ensembles (n = 1 -3) in PtxAg1-x/Pt(111) monolayer surface alloys, with 1 CO molecule per Ptn ensemble. Studies of the high-coverage regime are particularly interesting, since adsorption on spatially separated Pt ensembles may allow local coverages that are not accessible on active smooth surface such as low-index single-crystal Pt surfaces, where saturation COad coverages are in the order of 0.7 monolayers. As an extreme example, multicarbonyl species with more than one CO bound to a Pt atom had been proposed by Tsang et al. and Oduro et al. for Co-doped Pt catalysts. Combining these data with earlier results, we will also try to get further information on the role of electronic ligand and strain effects. Finally, aiming also at a more general understanding, we will compare the results obtained here with comparable data reported earlier for the structurally rather similar PdAg/Pd(111) system.