Three gold nanoparticle catalysts (differing in synthetic preparation) were characterized by examining the adsorption of CO on the surface of supported Au nanoparticles. Experimental methods using infrared spectroscopy were developed to determine the binding constant by varying the pressure of CO added to the catalyst sample at a constant temperature. A Langmuir-like analysis yielded binding constants that vary with CO coverage. These results along with temperature studies produced heats of adsorption that also varied with CO surface coverage. The three catalysts appear to have similar binding characteristics, with coverage dependent binding constants and heats of adsorption that are consistent with other studies.