Recently it was communicated that during gas-condensate production in a North Sea gasfield strong heating of the production stream occurred instead of the expected cooling. This contradictory behaviour called for an investigation of the thermodynamics of these gas­ condensate reservoirs. It is expected that due to the high pressure and high temperature conditions in these gas-condensate reservoirs (pressures of approximately 1000 bar and temperatures of 100-200 °C), the Joule-Thomson coefficient will have a negative value and thus heating will take place at expansion; this is called the Joule-Thomson inversion effect. To ensure a safe operation and to ensure that downhole and surface equipment is specified according to downhole temperatures, it is required that pressure and temperature profiles can be accurately estimated for future productions. The present work is a literature review of what has been reported in the open literature with respect to the Joule-Thomson inversion effect and the heating of gas-condensates at expansion. Chapter 2 will give a general introduction to the Joule-Thomson effect. In chapter 3 the various methods of how to characterize the inversion curve are described and chapter 4 will discuss the calculation of the temperature changes due to expansion. The gas-condensate systems are dealt with in chapter 5 and finally in chapter 6 a summary is given and different aspects, which are important to predict temperature changes for gas-condensate systems, are considered.