Three synthetic fuels, derived from coal, were compared to a Phillips DF-2 control fuel. These fuels were tested in a single-cylinder, direct-injected, Diesel engine. Comparisons were made on the basis of performance, combustion characteristics, gas-phase emissions including aldehydes, and particulate emissions. In addition, the mutagenic activity of the soluble organic compounds from the particulates were analyzed using the Ames test. The objective of these experiments was to determine how well the synthetic fuels would perform as direct replacements for DF-2.All three synthetic fuels were manufactured from an initial batch of middle distillates produced by the Exxon Donor Solvent (EDS) process. The first fuel was a blend of the EDS middle distillate and the baseline DF-2 with a cetane number of 35. For the second test fuel, the phenolics were removed from the EDS middle distillate by caustic extraction, and the product was then mixed with the baseline DF-2 to achieve a cetane rating of about 35. The third test fuel was obtained by severely hydrotreating the caustic-washed EDS middle distillate used to prepare the second fuel; its cetane number was 38.Overall, the hydrotreated EDS fuel gave the best results compared to DF-2. The raw EDS and caustic-treated EDS blends showed poor results, especially at light loads, compared to DF-2.