NOVELTY - The method involves compressing medium in liquid phase to obtain compressed liquid medium, heating the compressed liquid medium to expand the medium and obtain medium in supercritical state, reducing pressure of heated medium to a controlled degree by applying variable load to generate electric power of a frequency, converting the frequency to a desired output frequency, and reducing temperature and volume of medium to obtain the medium in liquid phase for recycling. The degree of compression of medium is controlled independently of the load applied in reducing pressure of heated medium.    USE - Extracting method for energy from low temperature energy source, such as exhaust gas or water.    ADVANTAGE - The method controls/balances pressure in number of positions in/segments of the system in order to efficiently convert the heat from a medium of relatively low-temperature, thus, pressure control is achieved without substantial energy losses. Need for energy-wasting valves to control the flow of medium that is heated by the external heat source becomes unnecessary. The amount of energy consumed by the motor of the pump to reach the pressure desired for heating is reduced.    DETAILED DESCRIPTION - The medium in liquid phase is compressed using an external power source. The compressed liquid medium is heated using heat partly derived from an external heat source. The external heat source is selected from exhaust gases, industrial cooling media, heated media from a solar collector, geothermal heat sources, ground water, sea water and fresh water. The medium is selected from carbon dioxide (CO2), ethylene (C2H4), diborane (B2H6), ethane (C2H6) and nitrous oxide (N2O). An INDEPENDENT CLAIM is also included for a heat engine system for extracting energy from an external heat source.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic piping and control diagram of a heat engine system.    Heat engine system (1)    Pump (22)    Motor (32)    Pressure sensors (500,502)    Control device/computer (504)