An engine unit, particularly for urban transport, comprising an engine (3) supplied with a compressed gas and having a expansion chamber (9), a liquid gas tank (28) in communication with the engine (3), and means (M, M′) for gasifying the liquid gas, which are interposed between the liquid gas tank (28) and the engine (3) for obtaining compressed gas. The gasifying means (M) comprise a gasification chamber (22) in communication with the liquid gas tank (28) and a liquid fuel tank (39) which is connected to the gasification chamber (22). The gasification chamber (22) is in fluid communication with both the liquid fuel tank (39) for the combustion of the liquid fuel with the oxygen of the liquid gas (22), and the expansion chamber (9) so that the compressed liquid gas and gaseous products of combustion process are used to do useful work.