Diesel
Diesel-fueled vehicles keep on trucking
Diesel fuel has a long history as an alternative to traditional gasoline, and is most-often associated with tractor-trailers, delivery trucks, military vehicles, helicopters and German automobiles.
Refined from petroleum, diesel fuel is less complicated and cheaper to produce than gasoline, though it has more impurities and doesn't burn as cleanly. The upside is that you get better mileage for less cost; the downside is that it's worse for the environment - beyond contributing to "smog," particulates released in diesel fumes are known to contribute to respiratory illnesses and contain cancer-causing elements.
From a practical perspective, diesel engines also require less maintenance and traditionally remain on the road longer than gasoline-powered engines. It is a preferred fuel for vehicles that tow or carry heavy loads (including pickup trucks). Diesel engines are typically noisier than gasoline engines, and still earn the stigma of being smellier!
The trucking industry has been moving to cleaner-burning, more efficient diesel engines, and installing devices that reduce emissions. Diesel fuel is being combined with biofuels to reduce toxic output, and more consumer vehicles - both light trucks and automobiles - are being built with diesel engines to take advantage of the increased fuel economy.
Diesel fuel is available at many gasoline stations, though not everywhere. It's always available at truck stops, though it is not currently available in hybrid vehicles.
Considering diesel as a vehicle fuel alternative is just OneThing you can do in your quest to help conserve resources and reduce our dependence on more costly energy sources such as oil and gasoline.