The phenomenon of cool flames can be used for mixing, evaporation, and overheating of a mixture of fuel, air, and steam. This method is used to provide a homogeneous mixture preparation. This study investigates the existence of cool flames running a stationary cool flame reactor under autothermal reforming conditions. It particularly characterizes the thermal limits of the cool flame reaction at high steam-to-carbon ratios. The experiments show that a cool flame vaporizer can be combined with an autothermal reformer leading to a homogeneous temperature profile in the front of the catalyst bed. This results in a good conversion of the fuel in the reforming process. (C) 2004 American Institute of Chemical Engineers AIChE J, 50: 1042-1050, 2004