Adsorption of carbon monoxide on a TiO2 (anatase) surface at room temperature has been studied by IR spectroscopy and volumetry. The obtained experimental data indicate weak adsorption of CO molecules on an exponentially inhomogeneous surface. It is established that adsorption heat decreases according to the logarithmic law with an increase in coating in the range of 0.002–0.03. Values of the extinction coefficient of adsorbed CO for a heterogeneous CO/TiO2 system are calculated using the Bouguer–Lambert–Beer law and taking into account the correction for the Lorentz field. Conditions of validity of the Bouguer–Lambert–Beer law for studying heterogeneous systems are described.