Synthesis of organic fuels from cain dioxide and hydrogen is analysed, in terms of energy recovery efficiency, and the required energy input for electrolysis of water. This electrical energy is related to the thermal energy required in a power station. A method is described to recover heat from energy-producing reactions in the fuel synthesis process, which can then be used to reduce the electrical energy requirement for electrolysis. By co-locating the fuel synthesis plant with a thermal power station, primary (thermal) energy can be used to produce high temperature steam, with a lower electrical requirement for electrolytic production of hydrogen. This can make more efficient use of the primary energy than a thermodynamic engine. Comparison is made with alternative fuels, in terms of energy budget, sustainability, carbon dioxide emissions, etc. The energy security benefits of advanced fuel synthesis are also identified.