If you've been to a cookout recently, you're probably familiar with our next alternative fuel: liquefied petroleum gas, or LP gas. Still not sure if you've seen it? Well, do you ever grill with propane?
Propane is the common name for liquefied petroleum gas, although that's not exactly right. LP gas is a hydrocarbon gas under low pressure. It's made up mainly of propane, but it also includes other hydrocarbon gases. LP gas is kept pressurized in order to keep it in liquid form. Similar to liquefied natural gas, keeping LP gas liquefied makes it more energy dense, and thus more useful for powering cars and trucks.
LP gas powers a car through an internal combustion engine that's been engineered for that type of fuel. While this type of fuel isn't widely used for cars in the United States, LP gas accounts for 10 percent of automotive fuel in the Netherlands, and lots of other counties have experimented with it, too [source: California Energy Commission].