Butane and propane are hydrocarbon gases which can be burned as fuel. Mixtures of these gases are commonly referred to as LPG, Liquified Petroleum Gas, because they are stored under pressure in liquid form. As a liquid, these gases are 270 times more compact than as a gas which allows them to be easily transported and stored. This property makes LPG a good substitute for natural gas in water heaters, stoves, and furnaces. Pressurized tanks or canisters of LPG mixtures can reach homes and businesses not served by natural gas companies. Some LPG is also transported as a liquid in pipelines, and large amounts can be shipped in specialized tankers. Approximately 15 billion gallons of propane are consumed annually in the U. S. as a fuel gas.

Unprocessed natural gas contains about 3 to 18 percent propane (C ₃H ₈), as well as some butane (C ₄H ₁₀). These two...