Energy comes from a Power Source. There are many types of power sources, but most energy we use today comes from an energy source known as "fossil fuels." Coal, crude oil, and natural gas are fossil fuels. These substances were formed when ancient plants and animals, like the dinosaurs, died. As their bodies decayed, they were mixed with the sand and mud, and buried deep in the earth. Compression and heat over millions of years changed them into substances that we can burn as fuel.