Three light-duty vehicles were measured on-board for their fuel consumption and regulated emissions while driven on diesel, pure rapeseed plant oil (PPO) and a 5% biodiesel (B5) mix with diesel. They were driven along a realistic cycle covering urban, rural and motorway roads. The vehicles were an Opel Vivaro 1.9 DTI Van, a Citroën Berlingo 2.0 HDI car and a Nissan Patrol GR 3.0 diesel SUV. Each vehicle was retrofitted with an Econet PPO two tank kit. They started on diesel when cold and switched to PPO -heated over a heat exchanger- when warm.As PPO has a lower caloric value compared to diesel fuel, consumption on PPO was higher. On B5 no significant effect was noticed. PPO however has lower carbon content and CO₂ emissions were a few percent lower than on diesel except for the Nissan Patrol where they were 8% higher. Carbon monoxide (CO) emissions were low on all fuels and showed no clear trend except for the Nissan Patrol that emitted three times more on PPO and for the Opel that emitted three times more on B5. The total hydrocarbon (THC) emissions were two to three times higher on PPO but at a very low absolute level. Nitrogen oxide (NOx) emissions were higher on PPO, from 9 to 56%. On B5 there was no significant effect. As to the Particulate Matter (PM) emissions a drop of about 50 to 60% was found. On B5 there was a drop of less than 10%.The Nissan Patrol in this study showed high CO emissions at idling when running on PPO. The engine management system was not able to correct this and produced a fault code indicating that the fuel was out of specification. Overall this vehicle was having higher fuel consumption and emissions on PPO than the other two vehicles. This indicates that not every diesel-fuelled vehicle can be easily converted to PPO with success.