An improved system of transferring heat energy from a high temperature fluid to a low temperature fluid is described. A countercurrent heat exchanger is employed in which heat transfer fluids undergo one or more thermodynamic transitions at various pressures by employing conventional heat exchangers having additional components. It has been determined that by employing this system of the present invention under a critical choice of design parameters, a substantially greater amount of heat energy can be transferred per unit area of the heat exchanger than was possible by conventional techniques.