The present paper describes the results of a research activity aimed to assess the potential of hydrocracked fossil oil (HCK) and Hydrotreated Vegetable Oil (HVO) blends, as future premium diesel fuels, on fuel consumption (FC) reduction of the modern automotive diesel engines. Three fuels have been formulated and tested in a light duty four-cylinder diesel engine, Euro 5 version, equipped with closed loop control of the combustion. The set of fuels comprised three experimental fuels formulated ad hoc by blending HVO and HCK streams, and an EN590-compliant commercial diesel fuel representative of the current market fuel quality. A specific test procedure based on a sequence of New European Driving Cycle (NEDC) and ARTEMIS cycles on an engine dyno test bed was applied in order to carry out accurate fuel consumption measurements versus fuel quality, so reproducing the fuel effects on FC for long mileage use of the vehicle. Results of the experimental activity proved that HCK-HVO blends give a benefit on both FC and CO2 saving. Taking into account the strong similarity in terms of combustion system design between Euro 5 and Euro 6 engines, the estimated trends can be considered valid also for Euro 6 vehicles equipped with the same class of engines. In a next step, it is planned to validate these results by carrying out also WLTP and RDE emission tests.