Results comparing fuel efficiency, pressure development history, gas phase emissions, and particulate biological activity for several nonpetroleum-based fuels with a standard number two Diesel fuel oil baseline are presented. In addition, a correlation based on ignition delay is presented which appears to more reliably reflect the combustion performance for these nonpetroleum fuels than does the cetane index.In this single-cylinder engine study, it was found that none of the fuels investigated showed a marked difference in fuel efficiency when compared to Diesel fuel oil. The same was not generally true for the exhaust emissions, where differences were found in the gas-phase as well as the particulate emissions. Most notable were the changes in the oxides of nitrogen and in the particulate generation rates. The oxides of nitrogen were fuel dependent as was the mass rate of particulate production and its soluble organic fraction. For each fuel, the mass rate of particulate generated turned out to be linearly dependent on the rate of fuel consumption.