The effects of reaction gases including CO2 and H2O and temperature on the selective low-temperature oxidation of CO were studied in hydrogen rich streams using a flow micro-reactor packed with a Pt-SnO2/Al2O3 sol-gel catalyst that was initially designed and optimized for operation in the absence of CO2 and H2O. 100% CO conversion was achieved over the 1 wt% Pt-3 wt% SnO2/Al2O3 catalyst at 110 degrees C using a feed composition of 1.0% CO, 1.5% O-2, 25% CO2, 10% H2O, 58% H-2 and He as balance at a space velocity of 24,000 cm(3)/(g h). CO2 in the feed was found to decrease CO conversion significantly while the presence of H2O in the feed increased CO conversion, balancing the effect of CO2.