This study compared diesel exhaust emission for a low sulfur and a Fischer-Tropsch (F-T) diesel fuel. The comparison included regulated emissions, airtoxics, aldehydes/ketones, and greenhouse gas emissions. Testing was conducted using a Cummins B-Series engine installed in a heavy light-duty truck operating on a chassis dynamometer and on an engine dynamometer. The chassis driving cycles included city, highway, and aggressive driving operation. Engine dynamometer tests included the U.S. transient cycle. Results showed that the F-T diesel fuel substantially reduced emissions although the engine was not specifically tuned to take advantage of the unique characteristics of F-T diesel fuel.