A gaseous fuel mixer for an internal combustion engine includes a frustoconical cone and an outlet element extending from the frustoconical cone at an interior portion of the frustoconical cone. The outlet element and the frustoconical cone are located within a mixer passage of an intake system. The mixer passage has an internal diameter. The outlet element includes a plurality of transverse openings that connect a fuel passage formed within the outlet element to the interior portion of the frustoconical cone. The height and diameter of the frustoconical cone and the internal diameter of the passage form specific ratios that provide for uniform mixing of intake air and gaseous fuel prior to the mixture flowing into an intake manifold of the engine.