Abstract: A compressor-expander assembly for use in a refrigeration system which includes a housing defining compression and expansion chambers of generally cylindrical section arranged side by side. Compressor and expander rotors of cylindrical shape are journaled for rotation in the respective chambers. The rotor shaft is offset from the chamber axis so that the surface of each rotor extends closely adjacent to the wall of the chamber causing each chamber to have a convergent side and a divergent side. Equally spaced about the rotor periphery are a set of vanes having their outer edges extending into engagement with the walls of the respective chambers so as to define a series of compartments of changing volume. The compression chamber has an arcuate inlet port which extends over substantially the entire divergent side and a concentrated outlet port which is located near the end of the convergent side.