Abstract: Specifically disclosed is a method of operating a vapor cycle engine wherein a vaporizable fluid is circulated in a closed loop serially through a first heat source, a second heat source, an expansion vapor engine, a condenser, and back to the first heat source. The method of operation specifically comprises the steps of heating the fluid in the first heat source to a relatively low temperature t, super-heating the fluid in the second heat source to a temperature T, passing the fluid through the expansion vapor engine and then exhausting the fluid from the engine at a temperature T.sub.2 which is greater than the temperature t. Also disclosed is apparatus for specifically accomplishing the method as disclosed.