Calgary Transit has been using low sulphur diesel fuel (50 parts per million) since 1994. The amount of sulphur in the diesel fuel Calgary Transit purchases is 1/10 the amount found at your local commercial diesel fuel outlet. The current generation of bus engines can handle this low sulphur fuel, and it is expected that the next generation of engines will be able to efficiently run on fuel with sulphur concentrations as low as 30 parts per million.

Sulphur burns in air to form the gaseous dioxide sulphur(IV) oxide, SO₂

S8(s) + 8O2(g)

8SO2(s)