The reactions of CO, NO, and oxygen on platinum surfaces have received a great deal of research attention, because of both their industrial importance in the three-way automobile catalytic converter and the academic interest surrounding the kinetic oscillations observed under some conditions. Crucial parameters in many of the kinetic models of these systems are the coverage-dependent heats of adsorption of the reacting species, which, with the exception of isosteric data for CO, have not previously been determined experimentally.Here the results of microcalorimetric measurements of the heats of adsorption of CO, NO, and O 2 as a function of coverage on Pt{110} are presented. The initial adsorption heats are 183, 160, and 335 kJ mol -1 , respectively.