A rotor (1) designed to be installed in the housing (16) of a free jet centrifuge, the rotor being provided with at least one inlet (3) and at least one outlet (4), which outlet is configured as a nozzle which is oriented at least substantially tangentially to the axis of rotation (13) of the rotor. The rotor is provided with receptacles for bearings for rotatably mounting the rotor, and the rotor having at least one guide element (7) which extends from an inner wall (38) to an outer wall (39) of a rotor interior space (8). At least the rotor shell (11) is made of synthetic resin material. Owing to its form, the synthetic resin centrifuge rotor can be made up of a reduced number of parts. The rotor may be composed of two elements, a base (10) and a shell (11), connected together either by a snap connection or by welding, such as vibration welding. An oil centrifuge fitted with such a rotor is particularly suitable for cleaning lubricating oil used in an internal combustion engine.