Abstract: A heat recovery system for the production of mechanical energy from a plurality of different heat sources at different temperatures comprises a plurality of heat exchangers associated one with each heat source, a plurality of circuits for a working fluid which traverses the heat exchangers, the circuits including expansion devices in which the working fluid is expanded and possibly vaporized to derive mechanical work from it, this being accompanied by a fall in temperature; the circuits for the working fluid have certain parts in common, such as the heat exchanger associated with the heat source at the lowest temperature, at least one of the expansion devices, a condenser in which working fluid vaporized in the expanders can be recondensed, and a circulation pump for driving the working fluid around the circuits.