Answer: It is clear that the fuels currently used will not be sustainable for the exponential growth of our energy demand. Although it is difficult to accurately predict the fuels that we will use, however it is clear that the powerful combustion of hydrogen is expected to be used especially to propel the aerospace and aeronautical industry. We can also highlight the use of nuclear fusion energy that until now is taking its first steps and finally it is quite likely that solar energy will continue to be used but in a much more powerfull and efficient way.