When renting autos in Diadal, clients get cars with a standard amount of fuel. This amount should be enough to drive to the nearest fuel station. Fueling the rented vehicle during the rental period is the responsibility of the driver; thus, it is paid separately. When the vehicle is handed back, the amount of fuel should correspond to the initial level.
Note that besides fuel, the driver is responsible for all sorts of damage connected to improper fueling. Thus, if some parts go wrong due to feeding cars with improper fuel, be ready to cover the cost of recovery.