LPG (Liquefied Petroleum Gas) means liquefied petroleum gas and it contains gases; mainly butane and in small proportions propane and butene. The gaseous mixture is liquefied under high pressure and filled in cylinders at high pressures. To known the leakage of the gas from the cylinder, methyl mercaptan having a very bad smell is mixed. LPG is mostly used as a household fuel.
CNG (Compressed Natural Gas) contains mostly methane and in some proportion ethane and propane are present. By reducing its volume at high pressures, it is used as a fuel in place of petrol in automobile engines like trucks, buses, etc. as CNG is completely combusted, the additional poisonous gas does not spread pollution but sometimes because of combustion, it heats up the mechanical machinery of the vehicle which is the disadvantage of CNG.