Propane is a gas that has been compressed into a transportable liquid form. Propane is made from other types of petroleum. It is often used as fuel for engines, stoves and more. The price of propane per gallon is difficult to pinpoint, as it changes on a weekly basis. Sometimes, it even changes on a daily basis. Recently, though, the average cost of propane has hovered around the $1.80 per gallon mark.