This paper studies the effect of space time on the deactivation of a Co/CeO 2 catalyst during oxidative steam reforming of ethanol. Increasing space time increased the ethanol conversion and hydrogen selectivity whereas acetaldehyde formation decreased. Both thermogravimetric and scanning electron microscopy analyses of post-reaction samples indicate that higher space times favor the deposition of filamentous carbon. However, the amount of carbon formed passes through a maximum and then decreases at high space time. Higher space times appear to allow the support, based on its oxygen mobility property, enough contact time to supply O needed to clean the carbon.