The majority of the sulfur in crude oil occurs bonded to carbon atoms, with a small amount occurring as elemental sulfur in solution and as hydrogen sulfide gas. Sour oil can be toxic and corrosive, especially when the oil contains higher levels of hydrogen sulfide, which is a breathing hazard.
The poor quality of crude oil currently can obviously result in the high sulfur contents of oil products, which can lead to corrosion, catalyst poisoning, environmental pollution and other negative consequences. The treatment of high-sulfur crude oil is becoming the focus of research in China's oil …
What is sulfur's purpose in engine oil? - Bob Is The Oil Guy
The sulfur content of most crude oil ranges from 0.1 percent (sweet grades) to 4.1 percent (sour grades).