The goal of the Clean Engine Vehicle project (CEV) was the conversion of a gasoline engine to dedicated natural gas operation in order to achieve a significant reduction in C0 2 emissions. The targeted reduction was 30% compared with a gasoline vehicle with similar performance. Along with the reduction in emissions, the second major requirement of the project, however, was compliance of the results with Euro-4 and SULEV emission limits. The project entailed modifications to the engine and the pre-existing model-based engine control system, the introduction of an enhanced catalytic converter and downsizing and turbocharging of the engine. As required by the initiators of the project, all components used were commonly available, some of them just being optimized or modified for natural gas operation. Such technology represents one of the cleanest powertrains for motor vehicles, especially if an effectbased assessment of exhaust emissions regarding greenhouse gases, ozone-forming potential, acid formation and toxic exhaust emissions is considered.