Abstract: The machine comprises a housing with parallel intersecting bores in which two pair of lobed rotors are rotatably mounted. The housing has high-pressure, end ports which are occluded and exposed by one rotor, i.e., a gating rotor, of each rotor pair. The gating rotors and their paired, co-acting rotors, i.e., main rotors, have different-sized hubs. The gating rotors have the larger-diameter hubs to control the high-pressure end ports. The rotor pairs are so configured and dimensioned as to insure that each pair defines a constant and uniform clearance therebetween in all rotary positions, and provide a machine having an optimum performance.