Propane (C3H8) - a colorless, flammable, liquefied gas. Pure propane is odorless so like natural gas it has Ethyl Mercaptan added which gives it its distinctive "smell". The most common cylinder sizes of propane are 33 lb for fork-trucks and 100 lb for heating/cutting. Many branches also offer BBQ cylinder refilling or exchange. Propane is also available in bulk from 500 gallon tanks all the way to 30,000 gallon tanks.