Abstract: The invention relates to a multi-fuel engine comprising a primary fuel supply and at least a secondary fuel supply. The primary and at least secondary fuels are arranged to mix with each other and with air for combustion in one or more cylinders of the engine in use. One or more electronic control units (ECU) are provided to control one or more supply characteristics of the primary and/or at least secondary fuel(s) in use. The engine includes a mass air flow (MAF) sensing means. At least one of the ECUs is arranged to receive one or more signals from the MAF sensing means to control, at least partially, one or more supply characteristics of the primary fuel. In addition, the ECU and/or a further ECU is arranged to receive one or more signals from the MAF sensing means to control, at least partially, one or more supply characteristics of the at least secondary fuel.