Why does natural gas smell so bad?

Gas odourant injection facility, Australia. Photo by Glen Dillon.

Natural gas doesn’t have a smell. What you smell is an odorant added by gas companies.  Why do they do this?

Natural gas has no color or odor, so it’s extremely hard for you to detect it.  Adding an odorant solves the problem.  

The most common odorants are thiols.  Thiols are sulfur containing compounds that are found in many unpleasant smelling things including rotten eggs, sewage, and skunk spray.  Thiols are sometimes called mercaptans.

Butanethiol, which smells like “skunk” and tetrahydrothiophene, which smells like rotten eggs, are the most frequently used as natural gas odorants.