Fossil fuels, especially oil and gas, are the major sources of heat for conventional gas turbines. The heating value of a fuel (Hf) is one of the most important factors to consider when choosing a fuel. Traditionally, gas turbines operate on high calorific fuels such as natural gas (Hf = 39–46 MJ kg−1) and Diesel no. 2 fuel oil (Hf = 42 MJ kg−1). A recent estimation of the reserves of fossil fuels shows that the production of these fuels will be constrained by the projected reserves. Consequently, there is a need to find alternative sources of energy, and biofuels are promising to be a sustainable option of supplying energy. Combustibility of biofuels has been demonstrated at laboratory and pilot scales. Nevertheless, combustion difficulties such as atomization and emission of NOx are still challenges to the wide-exploitation of biofuels in the gas turbine engines with the present combustion features. Nuclear energy is another possible source of heat for driving gas turbines but commercial nuclear power plants are commonly based on the steam Rankine cycle. Research work is going on in the area of high-temperature gas reactors for exploitation with closed cycle gas turbines.