Complete catalytic oxidation of 1075 ppm of vinyl chloride, trichloroethylene and perchloroethylene in humid (similar to 11 500 ppm water) air was studied over the temperature range of 250 to 400 degrees C. Three different catalysts, chromium exchanged zeolite Y (Cr-Y), cobalt exchanged zeolite Y (Co-Y) and cobalt impregnated gamma-Al2O3 (Co/Al2O3) were prepared and their activities investigated for the above reaction. Conversions varied from 1.6 to 100% with catalytic activities decreasing in the order : Cr-Y > Co-Y > Co/Al2O3. The adsorption capacity of the reactants also followed the same trend. The ability of chromium cation to exhibit multiple oxidation states coupled with its high ionization potential probably led to the higher activity of Cr-Y. The catalytic activity was found to diminish with increasing chlorine content of the reactant. Therefore, the catalytic activity decreased in the order : vinyl chloride > trichloroethylene > perchloroethylene. This phenomenon was attributed to the inductive and resonance effects of chlorine atom(s) on the electron density at the C=C bond. The zeolitic support produced higher activity than non-zeolitic because of the differences in the cation dispersion, acidity and redox potential of the cation.