The U.S. Bureau of Mines and Michigan Technological University are collaborating to conduct laboratory evaluations of oxidation catalytic converters (OCCs) and diesel fuels to identify combinations which minimize potentially harmful emissions. The purpose is to provide technical information concerning diesel exhaust emission control to the mining industry, regulators, and vendors of fuel and emission control devices.In this study, an Engelhard PTX 10 DVC (Ultra-10)* OCC was evaluated in the exhaust stream of an indirect injection Caterpillar 3304 PCNA mining engine using a light-duty laboratory transient cycle. This cycle was selected because it causes high emissions of particle-associated organics. Results are also reported for two different fuels with similar sulfur contents (0.03-0.04 wt pct) and a cetane number of 53, but different aromatic contents (11 vs. 20 wt pct).Samples were collected from a dilution tunnel to determine diesel particulate matter (DPM), DPM extractable organics, sulfates, and solids. Semi-volatile (vapor phase) hydrocarbons were collected on XAD-2 resin. In order to assess the overall effects on biologically active materials, organic extracts from the DPM and resin were assayed for selected mutagenic and carcinogenic polynuclear aromatic hydrocarbons (PAH) and for mutagenic activity.For both fuels, the OCCs significantly changed the concentrations of DPM and levels of extractable organics associated with both the particle and the vapor phase, with decreases from 30 to 60 pct. Particle and vapor phase-associated PAH concentrations and mutagenic activity were generally significantly changed by the OCC, with decreases from 20 to 70 pct. There were also some significant differences in DPM, solids, and mutagenic activity of emissions between the two fuels.We conclude that the use of modern OCCs in conjunction with low sulfur fuel has the potential to improve the quality of air in mines using diesels.