High selectivities and conversions in the preferential oxidation of CO in the presence of large quantities of H-2, H2O and CO2 are demonstrated on noble metal catalysts at millisecond contact times (similar to 10-15 ms) for temperatures between 150 and 500 degrees C. With a simulated water-gas shift product stream containing 0.5% CO and varying amounts of H-2, H2O and CO2, we are able to achieve similar to 90% CO conversions on a Ru catalyst at temperatures of similar to 300 degrees C using a stoichiometric amount of O-2 (0.25%). Experiments with and without O-2 and with varying H2O reveal that significant water-gas shift occurs on Pt and Pt-ceria catalysts at temperatures between 250 and 400 degrees C, while significant CH4 is formed on Ru and Rh catalysts at temperatures greater than 250 and 350 degrees C, respectively. The presence of H2O blocks H-2 adsorption and allows preferential CO oxidation at higher temperatures where rates are high. We propose that a multistage preferential oxidation reactor using these catalysts can be used to bring down CO content from 5000 ppm at the reactor entrance to less than 100 ppm at very short contact-times.