Particulate mass emissions (US-EPA FTP75) of a variety of light duty diesel (IDI) production vehicles have been analysed for their content of organic insoluble and organic soluble fractions. The latter was further separated into lube oil and fuel particulate fractions by a gas chromatographic method which is described in the paper. This has provided the information to establish a database on the relative contributions of organic solubles and lube oil to both total particulates and total hydrocarbon (HC) emissions. As a result a target minimum lube oil particulate emission level has been defined to act as a guide line in engine development to minimize the contribution of the lube oil to total particulate matter. Additionally, HC and the various particulate fractions of IDI and DI high speed diesel engines are compared under steady state and transient operating conditions and their relative significance indicated. Finally, the effect of engine design parameters mainly controlling lube oil particulates is quantified.