Gas engines that run on natural gas typically have a thermal efficiency between 35-45% (LCV basis).,[11] The best engines can achieve a thermal efficiency of slightly more than 48% (LCV basis). These gas engines are usually medium speed engines Bergen Engines Fuel energy arises at the output shaft, the remainder appears as waste heat.[8] Large engines are more efficient than small engines. Gas engines running on biogas typically have a slightly lower efficiency (~1-2%) and syngas reduces the efficiency further still.