Experiments were performed in an optically-accessible DI Diesel engine to investigate the effects of the addition of two oxygenated blending compounds to Diesel fuel, dimethoxymethane (DMM) and dimethylcarbonate (DMC). The focus of the study was to determine whether the structure of the oxygenated compound affects the production of soot. Laser light extinction was used to measure soot variation during combustion as well as exhaust soot levels. NOx, CO2 and CO concentrations in the engine exhaust were also measured using gas analyzers. Each oxygenated compound was blended into the base Diesel fuel to obtain 2% and 4% oxygen by mass. Heat release analysis showed that modifications of the heat release characteristics from those of the base fuel were significant, with increases of up to 1.7° in ignition delay and increases in the amount of premixed burn. The addition of the oxygenated compounds decreased the peak level of soot during combustion as well as the exhaust soot levels. For each level of oxygen addition, DMM was more effective than DMC at reducing soot. Reductions in NOx of 5 to 17% were also observed; no changes in CO levels were observed.