Quantity produced from propylene, which is a compound with the chemical formula C3H6. It is the second smallest compound in the alkene hydrocarbon group after ethane. It is gaseous at room temperature and normal pressure. It is colourless, flammable quickly, and has a garlic-like smell. It resides in coal gas and can be manufactured by braking down oil. The propylene is one of the most important elements of petrochemical industry. It is used as monomer, often for the manufacture of polypropylene.