Direct observation of dynamical equilibrium between preadsorbed CO and gas-phase CO is carried out by means of time-resolved infrared reflection absorption spectroscopy. For CO molecules on Ni(100) and on Pt(lll) surfaces, the temporal bimolecular CO cluster, adsorbed at nearby sites, exhibits repulsive interaction resulting in the enhancement in the desorption rate. Effective cluster formation may correlate with the accommodation time of an adsorbed molecule on a certain sire, i.e., the hopping rate of the individual adsorbed molecules on the surface.