The influence on regulated emissions of diesel fuel properties and composition has been investigated in an IDI passenger car fitted with EGR. The key findings were confirmed in limited tests on two other advanced technology European diesel passenger cars. This work is part of an on-going joint cooperative project involving Esso and Statoil.Tests on 37 fuels enabled the individual influence on emissions to be determined of fuel aromatics content, cetane quality, back end volatility (T95), density and sulphur content.This study reveals that the key fuel parameter influencing particulates in European diesel cars is density.In the typical European range of fuel densities (below 0.86 kg/l) there is a linear relationship between density and particulates. In this region T95 is also influential but increasing cetane number above 48 has negligible effect. Aromatics content is decisively shown to have no significant influence on particulates.The relationship between density and particulates becomes non-linear for fuels with higher densities (above approximately 0.86 kg/l). These produce an apparent overfuelling phenomena with a sharp increase in particulate and hydrocarbon emissions. In this region cetane number has a strong influence.Variations in natural and doped sulphur content produce an identical very small influence on particulate emissions in this non-catalyst passenger car.