Oxygen storage and its effects on the adsorbates during NO-CO reaction have been studied by sequential pulsing Of CO/O-2/CO into an NO-CO reactant stream over Pd/Al2O3 and Ce-Pd/Al2O3 catalysts. The adsorbates and reaction effluent were monitored concurrently by in situ infrared spectroscopy and mass spectrometry, respectively. It was found that the presence of ceria minimized the impact Of O-2 and CO on the adsorbates over the Ce-Pd/Al2O3 catalyst at 673 K. This effect diminished at 573 and 473 K along with its storage capacity. Storage capacity is directly proportional to temperature in the range 473-673 K. Oxygen storage occurs differently in the presence of NO-CO than in an inert helium/argon environment, which has been used widely as the medium to study 02 storage on ceria-based catalysts. The presence of the reactants and their adsorbates on the catalyst surface leads O-2 and CO to adsorb and react on the ceria surface prior to the Pd-0 surface at 673 K. In addition, O-2 pulses at 573 and 473 K, unlike those at 673 K, decreased linear/ bridged CO and linear NO on Pd-0 without producing Pd+-NO, indicating that oxygen blocks adsorption sites on Pd without oxidizing Pd-0 to Pd+. The active adsorbates for NO-CO decomposition are linear NO and linear/bridged CO on Pd-0.