A compact fuel processor for converting a hydro-carbonaceous fuel into hydrogen and carbon dioxide having in series a hydrocarbon conversion zone for converting the hydro-carbonaceous fuel into a product gas of carbon monoxide and hydrogen, a water-gas shift reaction zone containing a catalyst suitable for the water-gas shift conversion reaction, an auxiliary water-gas shift reaction zone containing a catalyst suitable for the water-gas shift conversion reaction, and a carbon monoxide removal zone. The invention further relates to a fuel cell system having such a fuel processor and a fuel cell and to the use of such a fuel processor or such a fuel cell system.