Together, gasoline and diesel fuel power 99 percent of this country's motor vehicle fleet. Past efforts to reduce vehicle emissions took petroleum fuels as a given and focused on the development of sophisticated engine and vehicle emission control systems involving catalytic converters, on-board computers, and other hardware. It is becoming apparent, however, that fuel composition and type are also critical factors in the clean vehicle equation. The Clean Air Act of 1990 explicitly recognizes that changes in fuels as well as in vehicle technology must play a role in reducing air pollution from motor vehicles. The recognition that fuels are significant opened up an interesting debate about the relative merits of petroleum and nonpetroleum fuels.
Petroleum fuels have many advantages as vehicle fuels.
Oil can still be discovered and pumped from the ground in many parts of the world for as little as ten or twenty cents per gallon. Gasoline and diesel fuel pack more energy per gallon than other fuels. On the other hand, petroleum fuels have certain drawbacks. Emissions of reactive hydrocarbons, carbon monoxide, and oxides of nitrogen from gasoline and diesel vehicles contribute significantly to the air pollution that plagues most large American cities. Carbon dioxide emissions from petroleum fuel combustion add to the atmospheric buildup of greenhouse gases and the potential for global warming.