Abstract: The invention is a venturi of unusual configuration and a method and apparatus for forming such a venturi in a single operation from a rounded, deformable tube. According to the invention, diametrically opposing sides of the tube are inwardly deflected in increasing amounts from opposing ends of the tube so as to form along the length of the tube from either end a first chamber of increasingly flattened and reduced cross-section followed by a second chamber of decreasingly flattened and reduced cross-section. An elongated throat section of maximally flattened and reduced cross-section may be provided between the first and second chambers, particularly for engine muffler venturis. The tube is conveniently deformed by applying pressure to a pair of its opposing sides along at least a portion of its length, preferably by pairs of opposing dies or eccentric rollers. Venturis for engine mufflers are conveniently fabricated from thin walled steel tubes by cold forming the tubes in the manner described.