A process for recovering waste heat which comprises: (a) passing a liquid phase working fluid through a heat exchanger in communication with a process which produces the waste heat; (b) removing a vapor phase working fluid from the heat exchanger; (c) passing the vapor phase working fluid to an expander, wherein the waste heat is converted into mechanical energy; and (d) passing the vapor phase working fluid from the expander to a condenser, wherein the vapor phase working fluid is condensed to the liquid phase working fluid. The preferred working fluid is an organic Rankine cycle system working fluid comprising compounds having the following general structure: ##STR00001## where x, y, z, and m are each selected from the group consisting of: fluorine, hydrogen, R.sub.f, and R, wherein R and R.sub.f are each an alkyl, aryl, or alkylaryl of 1 to 6 carbon atoms, and wherein R.sub.f is partially or fully fluorinated.