The heat of adsorption of benzene on clean Pt(111) at 300 K is measured calorimetrically and found to decrease with coverage (theta) as (197 -48theta - 83theta(2)) kJ/mol. Saturation coverage (theta = 1.0) is 2.3 x 10(14) molecules/cm(2). Sticking probabilities of benzene on Pt(111) were measured by mass spectrometry, giving an initial value of 0.97 and showing Kisliuk-type behavior with increasing coverage that implies there is a precursor to sticking with a ratio of its hopping rate to its desorption rate of similar to28. Benzene adsorbs transiently on the benzene-saturated surface at 300 K with a trapping probability of 0.90 and a heat of adsorption of 63-73 kJ/mol.