While petroleum is the most important energy source for our civilization, it isn’t the only one. Here are other energy sources and ways to transmit that energy, in particular electricity. In many discussions of energy, there’s a tendency to think of electricity itself as an energy source. Electricity is electrons flowing along a conductor from a source that has excess electrons to a destination with fewer electrons. The real energy source–burned hydrocarbons, moving water, nuclear fission, etc., has to free up the electrons and get them moving.