In the quest for cleaner air, there are numerous approaches in various stages of study, development and implementation. Despite stringent clean air regulations, which have reduced previously uncontrolled engine exhaust emissions by more than 10 fold, the population of pollution sources is growing faster than the reduction in the pollution rate per source. Various alternatives include cleaner fuels and alternative fuels, cleaner engines and alternative engines, as well as bold proposals such as electrical power or hydrogen as a fuel, which offer some measure of improvement. However, most efforts to date appear to fall in the category of too little, too late or too costly. It is concluded that a major changeover to natural gas as an alternative fuel for use in most engines, with a program that includes retrofit of old engines and modification of new engines to utilize natural gas, offers an effective and rational solution.