NOVELTY - A reformer comprises a venturi (12) through which the gas flow (11) passes, with liquid outlets (16a, 18a) discharging in the venturi throat.    USE - The unit is employed to atomize liquid feedstocks of a reformer, which supplies fuel cells with hydrogen.    ADVANTAGE - The unit provides a very high degree of atomization and mixing of water and liquid fuel. There is little delay in dosing them to the reactor. Good cold-start behavior is assured. Responsiveness to changing dynamic loads is secured. The requirements of the reformer at any instant are well-matched. No costly high pressure pumps are required; the liquids can be supplied at comparatively low pressure, taking advantage of the gas flow velocity. The Venturi, nested like Russian dolls, permit a largely unobstructed gas through flow, whilst providing good mixing for a comparatively low pressure drop.    DETAILED DESCRIPTION - Preferred Features: The venturi is located at least partially inside a gas pipe through which the gas flow from a supply line passes. The gas pipe forms a second venturi pipe in the region of the first. The first venturi is located inside the second, such that its outlet opening is located in the throat of the second. The gas pipe is at least partially within a further gas pipe of greater diameter, again passing the supplied gas flow. The further gas pipe forms a third venturi. Again the outlet of the second venturi is in the throat of the third (i.e. a set of nested Venturi is formed. The liquids supplied are water and/or a fuel. The supply lines (16, 18) are respectively for water and/or fuel. Their outlets in the first venturi, are directed against the flow direction of the gas. A spring-loaded non return valve is included in each fluid supply line, to prevent fluid dripping. This system may be designed in addition, as an oscillatory mass and spring system.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-section of a basic first venturi.    Gas flow (11)    Venturi (12)    Liquid outlets (16a, 18a)