Using classic thermodynamic principles as the point of departure, this book supplies the tools required to assess the technical viability of energy conversion processes. A new concept, viz. the exergetic (useful energy) recovery factor is introduced that measures net fraction of the extracted useful energy with respect to the initial exergy of the energy resource. With respect to conventional measures, the exergetic recovery factor can be negative, which indicates that more input exergy is required than extracted. A detailed description of the method will be given by applying it both to fossil fuel based energy resources and renewable energy resources. In addition a simplified procedure is given that gives the non-specialist reader the opportunity to judge both conventional and non-conventional energy resources. The case studies discussed comprise the conventional use of fossil fuel (oil gas and coal) the non-conventional use of fossil fuels (shale gas, underground coal gasification) and non-fossil fuel energy resources like geothermal, solar and wind. The book is an ideal guide for those engaged in the transition from fossil-based fuels to renewable and sustainable energy sources and who want to introduce technically viable new energy extraction technologies, which have a reduced carbon footprint.