Natural Gas is odorless. It is comprised mainly of methane which does not smell, however when you turn on the gas on your stove it gives off a very strong stench!
This is because of a chemical known as Mercaptan (also known as Thiol). This is added to Natural gas in order to make it smell! It is a harmless gas which is a waste product of normal metabolism and is found naturally in living organisms.
The chemical features very few useful qualities, bar one, it gives off an incredibly pungent smell. Even in the smallest quantities the human nose can still detect it. It is the world’s smelliest substance and is unbearable in its concentrated form.