The low boiling fraction of petroleum which leaves the fractioning tower as a gas is known as petroleum gas. Petroleum gas is a mixture of ethane, propane and butane. But the main constituent of petroleum gas is butane (C4H10).

The petroleum gas which is liquefied under pressure is called Liquefied Petroleum Gas (LPG). The liquefied petroleum gas consist mainly of butane,(with a very small amount of ethane and propane). Since the liquefied petroleum gas can be kept in the liquid form only under pressure hence LPG stored and supplied in gas cylinders. The gas cylinders were gat from the gas agency (Indane, Bharat, HP etc.)Contains liquefied petroleum gas (LPG).