Hybrid powertrains are an attractive option for vehicle manufacturers, with the potential to reduce fuel consumption, CO2 emissions and exhaust emissions of harmful compounds. However, laboratory procedures may not reveal the full picture regarding the performance of vehicles with hybrid powertrains compared to their conventional counterparts; even test procedures designed to test the environmental performance of hybrid vehicles may not accurately reveal the real world emissions performance. In this study, two vehicles were tested under real driving conditions with gaseous exhaust emissions measured using a portable emissions measurement system (PEMS). One of the vehicles featured a hybrid powertrain with a spark ignition internal combustion engine; the other vehicle featured a non-hybrid (conventional) spark ignition internal combustion engine. Aside from differences in the powertrain, the two test vehicles were of very similar size, weight and aerodynamic profile, meaning that the power demand for a given driving trace was very similar for both vehicles. The test route covered urban and extra-urban (but not motorway) conditions; the approximate distance was 12 km and the average speed was very close to 40 km/h. The test route featured multiple stop periods, little driving at constant speed (<10%) and several relatively rapid accelerations from standstill to speeds in the range 50-75 km/h, the latter being conditions under which fuel consumption, regulated exhaust emissions and the corresponding impact on urban air quality are typically high. Multiple differences in the emissions profiles of the two vehicles were observed: emissions of CO2 and all regulated gaseous exhaust emissions were lower in the case of the hybrid vehicle.