How is the energy from oil transmitted for use to humans?

Oil is a hydrocarbon fuel that contains carbon and hydrogen. When oil is burned, the carbon reacts with oxygen from the air to produce CO2 (carbon dioxide) and heat, while the hydrogen also reacts with oxygen to form H2O (water) and heat.

The heat comes from the formation of atomic bonds between these elements. The carbon-oxygen bonds were originally broken by the action of photosynthesis in plants using the Sun's energy and carbon dioxide from the atmosphere, so the process of burning oil releases that stored energy and also re-forms carbon dioxide.