NOVELTY - A process reforms liquid heating fuel oil (20) in the presence of a gas including oxygen. The fuel is first dispersed in an oxygenated gas jet (21') in conjunction with the admixture of a returned gas flow (3b) and evaporation of the fuel. The resulting gas mixture is partly oxidized in the presence of a heterogeneous catalyst to form a synthesis gas.    USE - Process to reform liquid fuel especially heating oil.    ADVANTAGE - The process eliminates the prior art difficulty of undesirable secondary exothermic processes.    DETAILED DESCRIPTION - The resulting synthesis gas is sub-divided into product (3a) and return-feed (3b) gas for re-circulation. Heat is abstracted (6) from the return-feed gas at a controlled rate to maintain the catalyst substrate (10) at a pre-determined temperature. The substrate (10) is a regular-shaped bulk solid with a high specific surface area. The mixture of fuel and gas is generated by a twin-jet array (2) with reduced pressure at the jet tip (23), resulting in a pressure gradient. The process makes partial use of the return-flow (3b) pressure. The substrate structure array is positioned to minimize flow-resistance and is preferably a honeycomb with parallel flow passages, a corrugated foil and cruciform flow channels, a reticular foam structure or a three-dimensional weave. De-ionized water is sprayed into the return-flow (3b) as a gas reactant and coolant. The oxygenated gas is introduced in two flows (21') by a pump. The first gas flow (21') is introduced into the heating oil spray (20'), while the second (22') is introduced via a jet (13) into the return-feed (3b). The gas employed is ambient air and/or effluent gas from an afterburner forming part of fuel cell battery. Also claimed is a commensurate assembly with a ceramic or metal catalytic substrate within a cylindrical tube (11) with a two-component jet (2) generating a mixture of heating oil and gas at a given distance from the catalyst body inlet (100). The gap is sufficient to allow the evaporation of the heating oil prior to admission, and spreads the mixture over the entire inlet surface area.    DESCRIPTION OF DRAWING(S) - The drawing shows an assembly for the process.    Two-component jet (2)    product (3a)    return-feed (3b)    cylindrical tube (11)    jet (13)    first gas flow (21')    second gas flow (22')    catalyst inlet (100)