The influence of pretreatment, gas composition and metal (Ce or Co) oxide promotion on the low-temperature CO and C3H6 oxidation activity over alumina-supported Pt and Pd has been studied. The monolith catalysts have either been preoxidised in O-2/N-2 Or prereduced in H-2/N-2 prior to evaluation with respect to light-off performance, using either net oxidising or net reducing CO/C3H6/O-2/N-2 gas mixtures. Compared with unpromoted Pt, promotion with preoxidised ceria or cobalt oxide enhances the low-temperature activity significantly and lowers the light-off temperatures by about 60-70 degrees C for both CO and C3H6. Prereduction of a cobalt-oxide catalyst (without precious metals) gives a dramatically improved performance compared with a preoxidised catalyst in terms of light-off and overall conversion. Prereduction of metal oxide promoted Pt and Pd can shift the light-off temperatures for CO and C3H6 by up to 100 degrees C toward lower temperatures compared with preoxidised samples. When using gas mixtures containing both CO and C3H6, the conversion of CO always starts at lower temperatures than the conversion of C3H6 The catalysts have been characterised by temperature-programmed desorption (TPD) of carbon monoxide, X-ray photoelectron spectroscopy (XPS), and specific surface area measurements (BET). The reduced cobalt containing samples adsorb large amounts of CO. The high activity over the catalysts containing prereduced cobalt oxide is suggested to be due to the presence of reduced cobalt-oxide sites on the surface of those samples.