An autothermal reformer is provided for a fuel cell system utilizing one volume and a plurality of inlets for both start-up and normal operation. In start-up mode, thermal combustion is employed for heating the catalyst reformation section of the reformer. Two inlets are used to feed air and fuel into the system, which are mixed and ignited in the common volume. Once the catalyst has reached light-off temperature, a second set of inlets provide air, steam and fuel into the common volume. The mixture then passes into the catalytic reformation system.