This study investigated the impact of varying natural gas composition on the exhaust emissions from a waste hauler equipped with a 2002 Cummins 8.3L, C Gas Plus, lean burn, spark ignited natural gas engine and an oxidation catalyst while operated on the William H. Martin Refuse Truck Cycle on a chassis dynamometer. The vehicle was tested on seven different fuel gas blends with varying compositions of light hydrocarbon species and inerts, resulting in different properties in terms of methane number and Wobbe number. The higher hydrocarbons gases exhibited higher fuel economy and CO2 (carbon dioxide) emissions. NOx (Nitrogen oxides) emissions were also impacted by fuel composition, and increased for gases with higher levels of heavier hydrocarbons. THC (Total hydrocarbons), CH4 (methane), CO (carbon monoxide), PM (particulate matter), and particle number emissions all showed some reductions for the gases with higher hydrocarbons, higher Wobbe numbers, and higher energy content. Formaldehyde and acetaldehyde were the most dominant aldehydes in the tailpipe, and decreased with the low methane number and high Wobbe number gases. Ammonia emissions did not show consistent fuel trends, however, ammonia emission levels were higher for the higher speed and load phase of the cycle. (C) 2012 Elsevier Ltd. All rights reserved.