NOVELTY - Reforming hydrocarbon fuel comprises: start-up phase comprising first stage (where hydrocarbon fuel is reformed in fuel reformer by exothermic catalytic partial oxidation process to hydrogen), second stage (where generated hydrogen is converted into water steam and fed back to reformer) and third stage (where endothermic catalytic steam reforming process is initiated in fuel reformer in which combination of exothermic and endothermic processes creates autothermal fuel reforming process (ATR)); and steady state operation phase (where hydrogen generated by ATR process is fed to fuel cell).    USE - The method is useful for reforming hydrocarbon fuel for generating hydrogen especially for operating a fuel cell (claimed), where the hydrocarbon fuel includes dimethyl ether, methanol, ethanol and propanol.    ADVANTAGE - The method needs no extra water from an external water supply.    DETAILED DESCRIPTION - Reforming a hydrocarbon fuel comprises: a start-up phase comprising a first stage in which the hydrocarbon fuel is reformed in a fuel reformer by an exothermic catalytic partial oxidation process to hydrogen, a second stage in which the generated hydrogen is converted into water steam which is fed back into the fuel reformer, a third stage in which an endothermic catalytic steam reforming process is initiated in the fuel reformer by the water steam, in which by the combination of exothermic and the endothermic processes an autothermal fuel reforming process (ATR) is created; and a steady state operation phase in which the hydrogen generated by the ATR process is fed to the fuel cell for operating the same. INDEPENDENT CLAIMS are also included for:    (1) arrangement for reforming a hydrocarbon fuel by the above method, for generating hydrogen for operating a fuel cell, where the arrangement comprises: a fuel reformer (1) containing an oxidation catalyst (1a), for generating hydrogen from supplied fuel and oxygen; and a catalytic combustion reactor (3), for catalytically converting hydrogen into water steam, where the fuel reformer and the combustion reactor are connected in a loop such that by the water steam from the combustion reactor an ATR can be created in the fuel reformer;    (2) control unit for controlling an arrangement;    (3) fuel cell system for generating power by means of at least one fuel cell, comprising an arrangement;    (4) computer program comprising computer program code means adapted to perform the method, when the program is run on a programmable microcomputer; and    (5) computer program product stored on a computer readable medium, comprising computer program code means.    DESCRIPTION OF DRAWING(S) - The figure shows a block diagram of the arrangement for presenting a first stage of the start-up phase of the method.    Fuel reformer (1)    Oxidation catalyst (1a)    Control unit (1d)    Gas clean-up reactor (2)    Catalytic combustion reactor (3)