The tables below explain how much energy the United States uses per source and where the energy is used. The United States used 99.2 quads of energy in 2009, where each quad equals one thousand billion BTUs. Electrical generation (39.97 quads) is very inefficient. Only 31.5 percent of the energy from the source (coal, natural gas, oil, nuclear) is transformed into electrical energy. The transportation industry is also wasteful in terms of energy, with 75 percent of the energy (mostly petroleum) it uses being wasted as heat.