Abstract: Internal combustion engine of the type comprising a pair of inlet valves per cylinder which are actuated by a single common rocker, the inlet ports formed by said valves and the relevant seats communicating with an external source of fluid via an induction duct formed in the cylinder-head of the engine. A respective induction duct is formed in the cylinder-head for each inlet port whereby these ports may, according to the mode of operation of the engine, be connected to corresponding external sources of gaseous fluid, for instance air and gas, or to a same source of gaseous fluid, for example air. This engine may be operated as a Diesel engine, or as a compound Diesel/gas engine, or alternatively as a gas engine, without requiring any replacement of the cylinder-head and/or the gear controlling the inlet valves.