This study aimed to investigate the characteristics of exhaust emissions and the fuel economy of a compressed natural gas (CNG) vehicle fueled with biogas and natural gases. A large CNG vehicle currently used as a city bus in Korea was tested on a chassis dynamometer under the European Transient Cycle (ETC) and the National Institute of Environmental Research (NIER) 06 cycles. One CH4-enriched biogas (97.6% CH4) and 5 natural gases with different CH4 contents (81.6-94.0% CH4) were used as test fuels. Total hydrocarbons (THC), CO, NOx and CO2 emissions in the NIER 06 cycle were higher than those in the ETC cycle for all tested fuels, while the fuel economy in the NIER 06 cycle was 43.7-51.5% lower than that in the ETC cycle. Total VOC emissions increased with increasing CH4 content in the fuel, with toluene being the highest proportion of the BTEX emissions in both the ETC cycle (72-80%) and the NIER 06 cycle (73-78%). Emissions of elemental/organic carbon exhibited a similar trend to that of nanoparticle emissions. Total organic carbon was mainly comprised of organic compounds at 97-99% (ETC cycle) and 95-99% (NIER 06 cycle). Polycyclic aromatic hydrocarbon emissions in the NIER 06 cycle were 133.3-577.8% higher than in the ETC cycle because of incomplete combustion and an increase in unburned fuel in the NIER 06 cycle, which is a low-speed driving mode. Nanoparticle number concentrations were lowest for M91 among the 6 tested fuels; the total number of particles in the NIER 06 cycle was 33.2-123.8% higher than in the ETC cycle. (C) 2014 Elsevier Ltd. All rights reserved.