We report the results of our study of the catalytic oxidation of carbon monoxide by a composite oxide catalyst containing one to one molar ratio of silver and cobalt. XRD, XPS and TGA studies indicate that the composite oxide is not a physical mixture of silver and cobalt oxides and that silver is stabilized in an oxide in the presence of cobalt at temperatures as high as 800 degrees C. Low temperature activity of the composite oxide compares very favorably to the previously studied low temperature CO oxidation catalysts. CO oxidation activity of the catalyst is reversibly degraded below 100 degrees C by the presence of excess CO2 and water vapor in the feed. IR spectroscopy shows that CO2 and water vapor adsorb weakly on the catalyst surface and thus may physically block access to CO and oxygen. IR spectra also showed that under reaction conditions CO does not chemisorb and at 50 degrees C or higher there are no carbonate species on the catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.