The physical characteristics of and oxidation rate for diesel particulates formed during combustion of fuel which contained lead were studied. The particulate matter was first collected on a filter installed in the exhaust line of a divided-chamber diesel engine and was then oxidized in a flow reactor. The conditions in the flow reactor simulated those which occur during regeneration of a typical experimental particulate trap in a vehicle.The chemical form of the lead in the particulate was lead sulfate. Electron microscopy showed that the lead was present at discrete locations in the particulate and that the size range of the quasi-spherical carbon particles in the particulate was not affected by the presence of lead during combustion. The variation of the specific surface area with the amount of carbon oxidized implied that during oxidation, the diameter of the carbon particles decreased.The order and rate of reaction between solid carbon in the particulate and oxygen were determined in the temperature and oxygen partial-pressure ranges of 690-740 K and 0.02-0.21 atmospheres (2-21 kPa), respectively. For these conditions, sample oxidation was kinetically controlled. The measured order of the reaction was 0.5, and the reaction rate was correlated with an Arrhenius expression.