A colorless gas with an offensive stench that is said to smell like rotten eggs. The gas can be detected at a level of 2 parts per billion. It is measured by a hydrogen sulfur analyzer. Natural gas contains up to several percent of hydrogen sulfide and as such are called sour gas wells from their offensive stench.

The intention of the hydrogen sulphide (H2S) specification is to prevent excessive quantities of this odorous, corrosive and toxic component entering the INGL pipelines.