A novel Rankine cycle system configured to convert waste heat into mechanical and/or electrical energy is provided. The system provided by the present invention comprises a novel configuration of the components of a conventional Rankine cycle system; conduits, ducts, heaters, expanders, heat exchangers, condensers and pumps to provide more efficient energy recovery from a waste heat source. In one aspect, the Rankine cycle system is configured such that three distinct condensed working fluid streams are employed at various stages in the waste heat recovery cycle. A first condensed working fluid stream is vaporized by an expanded first vaporized working fluid stream, a second condensed working fluid stream absorbs heat from an expanded second vaporized working fluid stream, and a third condensed working fluid stream removes heat directly from a waste heat-containing stream. The Rankine cycle system is adapted for the use of supercritical carbon dioxide as the working fluid.