The driving style is a crucial variable for real-world vehicle energy performance. This study uses a state-of-the-art methodology to separately assess its impact on the energy consumption. A benchmark driving cycle is modified according to specific driving styles, and the corresponding energy consumption is theoretically simulated. The driving style characterisation includes acceleration, braking and gear-shifting patterns for each driver through ad-hoc metrics. The methodology establishes a comparative analysis regarding the energy impact of a pool of drivers. Furthermore, the variability of a driver’s consumption on different vehicle technologies is assessed by considering an internal combustion engine- (ICE) vehicle and a plug-in hybrid electric vehicle (PHEV). The results reveal that each driver exhibits characteristic and heterogeneous acceleration and braking styles, with the gear-shifting style playing a significant role in the vehicle’s fuel consumption. From a policy perspective, this work contributes in the understanding of the discrepancies in energy consumption between officially reported values and the real-world performance.