Particulate matter in the air has become the focus of increased attention due to the concern of potential health effects. Among other sources, automotive vehicles are seen as a major contributor of fine particles. At present there is limited information available relating either to the number or size distribution of automotive particle emissions and detailed evidence has still to be established. To develop an understanding in the area of automotive particulate emissions a programme was carried out concentrating on tailpipe emissions as measured at the regulated particulate sampling point in a dilution tunnel.A previous literature study by CONCAWE had identified analytical techniques considered to be suitable for this application and which are capable of measuring both mass and number size distributions. Several variations of these techniques are available in the research field and the programme aimed to assess and compare their operation and performance.Four Diesel and three gasoline vehicles were tested, using a limited fuel matrix and varied driving conditions. In general, gasoline particulate emissions (mass and number) were lower than those for Diesel, but at high speed the numbers emitted were similar. More than 85% of all particulate mass (99% by number) were smaller than 1μm. The largest difference in particulate number emissions was apparent in gasoline versus Diesel technology. Vehicle effects were observed within the gasoline car set only. No significant fuel effects were identified on the particulate number emissions.