The oxidation of carbon monoxide on a Pd(100) single-crystal catalyst was studied using an elevated-pressure IR cell/ultrahigh vacuum surface analysis system. The kinetics of the reaction was followed by monitoring the total pressure change during the course of the reaction. Simultaneously, the surface concentration of adsorbed CO was measured using IR reflection absorption spectroscopy. An activation energy of 29.4 +/- 0.3 kcal/mol was found between 500 and 575 K at a total pressure of 1.50 Torr and CO/O2 = 2. The IR data obtained under reaction conditions show the CO coverage to vary between 0.45 and 0.55 monolayers (ML). For this coverage regime, the CO heat of adsorption was determined to be 29 +/- 2 kcal/mol, corresponding closely to the apparent activation energy. Between 0.5 and 10.0 Torr, negative first-order CO and positive first-order oxygen pressure dependencies were measured, yielding a zero-order total pressure dependence of the reaction rate. No change in CO coverage was observed with a change in the oxygen pressure, while the CO coverage increased from 0.50 ML at P(CO) = 0.50 Torr to 0.55 ML at P(CO) = 8.0 Torr.