Experiments were performed in an optically-accessible DI Diesel engine to investigate the effects of the addition of oxygenated blending compounds to Diesel fuel. The focus of the study was to determine how the structure and boiling point of the oxygenating compounds affect the emissions of NOx and soot. NOx, CO2 and CO concentrations in the engine exhaust were measured using gas analyzers. Laser light extinction was used to measure time-resolved, in-cylinder soot concentrations. Two different oxygenate families, maleates and glycol ethers, were chosen to study the effects of molecular structure on emissions. For both families, oxygenates of various boiling points were examined within the distillation range of the base Diesel fuel. All oxygenates were blended into the base Diesel fuel to obtain two percent oxygen by mass. Since the oxygenates were blended with the base fuel at a relatively low volume percent, modifications of the heat release characteristics from those of the base fuel were small. However, injection timing was varied with the base fuel to match the start of combustion of the oxygenated fuels in an attempt to compensate for the heat release effects on emissions. For the conditions of this study, both the maleate and glycol ether compounds reduced the soot in the engine, but the maleates appear to be more effective. The maleate compounds reduced NOx as well, apparently because they delayed the start of combustion slightly. No effects of boiling point were found for either family of compounds.