The document discusses various energy sources that have been or could be used for transportation and everyday life. It outlines biomass, hydropower, coal, petroleum, natural gas and nuclear fission as historical energy sources. It then examines alternatives to petroleum such as oil shale, coal liquefaction, and biodiesel. Finally, it analyzes options for fueling vehicles, including compressed natural gas which can power a vehicle for up to 300 miles with 80% lower emissions, and hybrid gasoline-electric vehicles which increase overall efficiency by almost 40% through regenerative braking.