Propane (molecular formula C3H8) is normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for residential central heating, engines, oxy-gas torches and portable stoves.
Propane is a clean-burning nonrenewable fossil fuel. Like natural gas (methane), propane is colorless and odorless. Although propane is nontoxic and odorless, foul-smelling mercaptan is added to it to make gas leaks easy to detect.
In North America, local delivery trucks with an average cylinder size of 3,000 US gallons (11,000 L), fill up large cylinders that are permanently installed on the property, or other service trucks exchange empty cylinders of propane with filled cylinders.
Heating oil is a low viscosity, liquid petroleum product used as a fuel for furnaces or boilers in buildings. Home heating oil is often abbreviated as HHO.
Heating oil is known in the United States as No. 2 heating oil. In the U.S., it must conform to ASTM standard D396.