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A key element of diesel emission control is reduction of the particulate or soot that is emitted by diesel engines. These particulates are made up of a carbonaceous fraction, a volatile organic fraction, and a sulfate fraction. In this study, the role of flow-through oxidation catalysts on the control of each of these fractions is reported. Laboratory and vehicle studies were made to investigate the importance of catalyst washcoat and noble metal composition as well as vehicle operating conditions on the control of the various soot fractions. The effects of exposure of catalysts to high levels of sulfur were also examined. An optimized catalyst was found to provide good control of the volatile organic fraction and sulfate fraction of diesel particulate emissions. For control of sulfates, silica is preferred over alumina as the washcoat and palladium is preferred over platinum as the noble metal. At higher temperatures, release of sulfate is thermodynamically controlled to low levels.