NOVELTY - Catalytic partial oxidation of a liquid hydrocarbonaceous fuel, involves mixing hydrocarbonaceous fuel with molecular oxygen to form a first mixture; evaporating the fuel by igniting the first mixture; mixing the evaporated fuel with molecular oxygen to form a second mixture; and contacting the second mixture with a partial oxidation catalyst for conversion into a product gas comprising at least hydrogen.    USE - For catalytic partial oxidation of a liquid hydrocarbonaceous fuel e.g. diesel fuel (claimed) to produce a fuel gas (e.g. hydrogen or hydrogen-rich gas mixture) for fuel cells such as solid oxide fuel cells or proton exchange membrane fuel cells.    ADVANTAGE - In the method the fuel is evaporated and preheated to 300 - 500degreesC before it contacts the partial oxidation catalyst, thus the necessary heat is generated with the fuel itself. Thus there is no separate, voluminous heater unit is needed, even if the inlet gas has a relatively low temperature, such as 200degreesC or even ambient (preferably 20degreesC). The reaction of the fuel with the first amount of molecular oxygen can be initialized and sustained even at fuel and molecular oxygen supply temperatures as low as ambient temperature, at fluctuating molecular oxygen supply, e.g. when using diesel exhaust gas as molecular oxygen source, and at fluctuating fuel supply. The method facilitates energy-efficient operation and reduces the formation of carbonaceous fuel residuals. The fuel is introduced with the first mixture, thus there is no need for several fuel supplies.    DETAILED DESCRIPTION - Catalytic partial oxidation of a liquid hydrocarbonaceous fuel, involves mixing hydrocarbonaceous fuel with molecular oxygen to form a first mixture; evaporating the fuel by igniting the first mixture; mixing the evaporated fuel with molecular oxygen to form a second mixture; and contacting the second mixture with a partial oxidation catalyst for conversion into a product gas comprising at least hydrogen. The overall oxygen to carbon ratio is 0.3 - 0.8 (preferably 0.40 - 0.75, especially 0.45 - 0.65). The oxygen to carbon ratio in the first mixture is 0.01 - 0.4 (preferably 0.01 - 0.15, especially 0.02 - 0.10).