The ~teractions of 02 and N20 in the low pressure range with a Cu(ll1) surface and of CO with adsorbed oxygen have been studied with ellipsometry, Auger electron spectroscopy and LEED. The adsorption of 02 was investigated in the 10-6-104Torr range and at crystal temperatures ranging from 23 to 4OO'C. 02 chemisorbs dissociatively with an initial reaction probability of about 10m3 and an apparent activation energy of 2-4 kcal/mol, which depends on the substrate temperature, up to a saturation coverage of 0.45. The probability of decomposition of N20 is 10ms at 300°C, and the activation energy is 10.4 kcal/mol For 250 < T< 4OO'C. The oxygen coverage saturates at B = 0.45 as well. For both oxidation reactions the kinetics can be described with a precursor state model. With LEED no superstructures were observed. The probability of the reaction of CO with adsorbed oxygen is 4 X lo-' at 250°C and is initially independent of the oxygen coverage. The reaction is assumed to proceed via a Langmuir-Hinshelwood mechanism. The activation energy for the reaction COad + oad -+ CO* is 18-20 kcal/mol.