Apart from the introduction of renewable fuels, improved engine efficiency is a useful strategy for the reduction of CO2 emission from vehicles. Therefore, this work deals with the catalytic on-board upgrading of commercial gasoline to enhance the content of aromatics, leading to improved knocking behavior to allow higher compression in the engine. Resulting from theoretical considerations and thermodynamic calculations, model mixtures with a higher aromatic content were prepared and analyzed towards their octane number. Engine tests with these mixtures show an enhancement of engine efficiency. Laboratory-scale catalytic reforming experiments demonstrated a relative increase of the aromatic content in the treated gasoline. The gaseous cracking products have good knocking behavior and could be routed to the engine as additional fuel.