As produced, pure natural gas is colorless, tasteless, and odorless. Most consumers find the odorless property surprising since they typically associate natural gas with the unmistakable smell of rotten eggs or rotting cabbage. That telltale odor, however, is man-made, resulting from the deliberate addition of small amounts of sulfur-containing compounds to impart the distinctive odor. The family of chemicals most commonly used are known as thiols (organosulfur compounds that are also often referred to as mercaptans), and the reason for "odorizing" natural gas is safety, to assist in alerting that a leak is taking place before dangerous concentrations of gas can build. This approach in the U.S. resulted from a catastrophic natural gas explosion that took place over 82 years ago.

In 1937, the London School of New London, Texas experienced a disastrous explosion that, according to their website, killed 293 students and teachers. The cause was a deadly build-up of odorless natural gas in a large dead-air space beneath the school that was subsequently ignited by sparks from a sanding machine. The force of the resulting explosion was powerful enough to lift the entire school building before it crashed down and destroyed the structure's main wing, with reports of the explosion being heard more than 4 miles away. In the aftermath of this disaster, the Texas State Legislature quickly passed a law requiring that thiols be added to natural gas to make leaks more readily detectable. This safety measure soon spread worldwide and continues today.

More information on the New London School explosion can be found on various Internet sites, including Wikipedia.