Abstract: A rotary machine in which plural, non-cylindrical rotors are provided for rotation within partially overlapping cylindrical bores, formed within a machine housing. Each rotor each said rotor has a curved outer surface formed of a plurality of contiguous mutually tangential curved portions.* The rotors are eccentrically mounted for synchronized, same directional rotation, within their respective bores, and each is arranged to alternately provide intake and exhaustion of working gaseous fluids, such that each rotor is continually either admitting or exhausting a working gas. The machine is constructed such that the rotors are cylindrical, each being of internally balanced form. The rotors do not touch each other or any portion of the machine casing at any time, while being positioned so as to define minimal gaps therebetween. A high rotational speed may be developed, thereby obviating the need for seals entirely, and thus further increasing the available speed, and thus the work efficiency of the machine.