Abstract: Improvements in the attenuation of sounds emitted by an internal combustion engine exhaust system are achieved by shaping a muffler housing to substantially eliminate flat sound radiating surfaces, providing a circuitous exhaust gas flow path within the muffler housing and around an imperforate barrier and providing an exhaust gas outlet from the muffler housing which extends generally perpendicular to the direction of sound propagation within the housing near that outlet. The housing may be generally ellipsoidal in shape having a non-zero curvature which varys in a continuous manner at substantially all points on the surface and, subject to that requirement, designed to have a generally maximal volume subject to the dimensional constraints of its environment.