The adsorption of CO on alumina supported metal (Rh, Ru, Pt and Pd) catalysts was studied by microcalorimetry and infrared spectroscopy. The correlation of the results obtained from these two techniques provides information about the CO adsorbed species and the variations in the site energy distribution. Using these methods the nature and number of the surface sites on metal clusters, including aspects such as the presence of edge, corner or step atoms or the type of exposed crystalline planes, can be determined. Furthermore, the energetic distribution of surface sites has been shown to depend on the metal loading.