NOVELTY - A direct oxidation fuel cell system (50) comprises a converter (33) for catalytically converting a portion of an unreacted fuel to liquid and gaseous products. An inlet of the converter is in fluid communication with a first outlet of liquid/gas separator (28) for receiving the portion of the unreacted fuel. A first outlet of the converter is in fluid communication with an inlet of the liquid/gas separator for supplying the separator with the liquid product. A second outlet of the converter supplies exhaust gas(es) to the atmosphere.    USE - Used as direct methanol fuel cell (DMFC) system for use in portable and mobile applications (e.g. notebook computers, mobile phones, and personal digital assistants).    ADVANTAGE - The DOFC system operates efficiently on highly concentrated fuel (i.e. above 17-25 M neat methanol) with high energy conversion efficiency, and retains all advantages associated with DOFC cells and systems, including space reduction leading to compact design, easy fuel storage/handling, and high energy density of the liquid fuel. The amount of undesirable substances contained in the exhaust gases from the DOFC system is minimized. The oxidant (e.g. air) flow rate can be increased, because an increased amount of liquid (e.g. water) is produced in the fuel cell, leading to an improvement in cell electrical performance and power output.    DETAILED DESCRIPTION - A direct oxidation fuel cell (DOFC) system comprises at least one fuel cell assembly including a cathode (14) and an anode (12) with an electrolyte positioned between them, the fuel cell assembly performing selected electrochemical reactions at the anode and cathode; a source of concentrated liquid fuel in fluid communication with an inlet of the anode; an oxidant supply in fluid communication with an inlet of the cathode; a liquid/gas (L/G) separator in fluid communication with outlets of each of the anode and cathode for receiving unreacted fuel and liquid and gaseous products of the selected electrochemical reactions at the cathode and anode; and a converter for catalytically converting a portion of the unreacted fuel to the liquid and gaseous products. An inlet of the converter is in fluid communication with a first outlet of the L/G separator for receiving the portion of the unreacted fuel. A first outlet of the converter is in fluid communication with an inlet of the L/G separator for supplying the L/G separator with the liquid product. A second outlet of the converter supplies exhaust gas(es) to the atmosphere. A first inlet of the converter is in fluid communication with an outlet of the anode. A second inlet of the converter is in fluid communication with the oxidant supply. An INDEPENDENT CLAIM is included for a method of operating a DOFC system.    DESCRIPTION OF DRAWING(S) - The figure is a simplified, schematic illustration of DOFC/DMFC system.    Anode (12)    Cathode (14)    Liquid/gas separator (28)    Converter (33)    Direct oxidation fuel cell system (50)