Strong Lewis acidity of a phase-pure gamma-Ga2O3 Was studied by the adsorption of CO at ambient temperature, with the combined use of adsorption microcalorimetry and in situ Fourier transform infrared spectroscopy. The concentration of strong Lewis acid sites turned out to be quite low, but it grew fast with increasing surface dehydration upon thermal treatments in the 573-773 K range. Two main families of Lewis acid sites were observed, characterized by rather different molar adsorption heats and CO stretching frequencies. These acid sites have been ascribed to coordinatively unsaturated Ga3+ ions located in defective (higher nu(CO)) and regular (lower nu(CO)) crystallographic sites, respectively. The possibility of extracting, for the CO/gamma-Ga2O3 system, quantitative information from the IR spectroscopic data is discussed in some detail.