Particle emissions from vehicles are currently under close scrutiny with respect to their contribution to ambient air quality relative to other sources. Small particles, less than 10 μm, referred to as PM10, have been linked to various health issues. In this study, tests have been performed on European diesel light duty vehicles using a range of production diesel fuels. Tests were also performed on two gasoline passenger cars for comparison. Measurements were made of exhaust particle size distribution and number, as well as mass emissions using the legislated filter paper method. The results showed that most of the particles emitted were very small, with median size of the order 100 nanometres (nm). The median particle size was insensitive to changes in fuel, vehicle or operating condition. Measurements of particle number broadly correlated with particle mass emissions, and ranked fuels and vehicle types in the same order. Under urban driving conditions, the gasoline TWC car had extremely low particulate emissions, while the non-catalyst gasoline car had emissions around 50% of those from the best diesel vehicle tested. At highway speeds, the number of particles per km emitted from the TWC car were similar to those from the non-catalyst car. Further work is needed to understand these results.