Better understanding of the interactions of pure and alloy catalysts are pertinent for designing the next generation direct alcohol fuel cell catalysts with improved performance. In this study microcalorimetric measurements of carbon monoxide, hydrogen, oxygen, and ethanol were performed on 5%Pt/γ-Al2O3 with Pt:Sn ratios varying between 1:0 to 15:1. The catalysts were prepared by incipient wetness impregnation of PtCl2(NH3).2H2O and SnCl2.2H2Osalts. Microcalorimetric measurements were performed at 323 K by using a Tian-Calvet type heat flow calorimeter (Seteram C-80) connected to a gas handling system and a volumetric adsorption apparatus employing Baratron capacitance manometers in the range of 10-4-10 Torr for precise pressure measurement. The amount of Sn was adjusted to obtain Pt:Sn ratios varying between 1:0 to 15:1. It was observed that the addition of Sn caused the loss of adsorption sites on (111) planes more severely than on (100) planes of the bimetallic clusters as monitored by CO adsorption differential thermograms. For hydrogen an opposite trend was observed, probably caused by chemisorption in subsurface layers of (111) planes. Alloying effects could be observed from the initial heats of adsorption of all of the adsorbates. The saturation coverages of all of the adsorbates decreased with increasing Sn loading while the defect site concentrations were not influenced much. Microcalorimetric studies on carbon supported Pt-Sn and Pt-Ru bimetallics will also be presented.