Fuel gas is a type of gas that is used as a fuel source. It is composed of hydrocarbons, which are molecules made up of hydrogen and carbon atoms. The four most common fuel gases are ethane (6 letters), METHANE (7 letters), propane (7 letters) and BUTANE (6 letters). Ethane is a colorless, odorless gas that is found in natural gas and petroleum. METHANE is the main component of natural gas and is also found in coal deposits. Propane is a colorless, odorless gas that is used in many industrial and commercial applications. BUTANE is a colorless, odorless gas that is used in lighters and camping stoves. All four of these fuel gases are flammable and can be used as a fuel source.