NOVELTY - An autothermal reformer assembly comprises an air/fuel/steam mixing station including transfer tubes extending through a manifold from an inlet chamber to an inlet end of a catalyst bed. The transfer tubes have gas entry passages interconnecting the interior of the tubes with the manifold.    USE - Reforming light hydrocarbon fuels, e.g. methanol, ethanol, gasoline and diesel fuel, and converting them to a hydrogen-rich fuel stream for use in a fuel cell power plant. It is also useful in vehicular applications.    ADVANTAGE - The assembly ensures a homogeneous mixture of air, steam, and fuel at the entrance of the catalyst bed at a minimum pressure drop. A mixing efficiency greater than 90% can be obtained.    DETAILED DESCRIPTION - An autothermal reformer assembly includes a catalyst bed (8) including an inlet end. The assembly also includes an air/fuel/steam mixing station adjacent to the catalyst bed inlet end. The mixing station includes an inlet chamber (22), a manifold (24) interposed between the inlet chamber and the catalyst bed inlet end, and cylindrical transfer tubes (26). Each transfer tube has a diameter and a centerline axis, and extends through the manifold from the inlet chamber to the catalyst bed inlet end. The assembly also includes gas entry passages (28) in sidewalls of each transfer tube. Each gas entry passage has an axis which is perpendicular to the centerline axis of the transfer tubes. Each gas entry passage is spaced apart from the catalyst bed inlet end by a distance which is at least two times the diameter of the transfer tubes. The assembly also includes a gas inlet passage (12) opening into the inlet chamber, and a gas inlet passage (14) opening into the manifold.    An INDEPENDENT CLAIM is also included for a method of mixing a fuel/steam gas with an oxidant gas using the hydrocarbon fuel autothermal reformer assembly, in which the method includes introducing a vaporized fuel/steam mixture into one of the inlet chamber and the manifold, introducing an oxidant gas into the other of the inlet chamber and the manifold, causing one of the fuel/steam mixture and the oxidant gas stream to flow axially through the transfer tubes towards the catalyst bed inlet end, causing the other of the fuel/stream mixture and the oxidant gas to flow from the manifold radially into the transfer tubes through the gas entry passages, and maintaining a pressure differential between the interior of the transfer tubes and the manifold which will result in the radially flowing stream entering the transfer tubes to be entrained and deflected into the axially flowing stream in the transfer tubes before/when the radially flowing stream penetrates the interior of the transfer tubes a distance which is about one-half of the radius of the interior of the transfer tubes.    DESCRIPTION OF DRAWING(S) - The figure is a schematic fragmented cross-sectional view of the mixing station.    Catalyst bed (8)    Gas inlet passage (12, 14)    Inlet chamber (22)    Manifold (24)    Transfer tubes (26)    Gas entry passages (28)