Sour crude oil contains high quantities of which substance?

Sour crude oil is characterized by the presence of significant amounts of hydrogen sulfide (H₂S). This compound is a toxic gas that not only contributes to the sour taste of the oil but also poses safety and health risks during extraction, transportation, and processing. The high concentrations of hydrogen sulfide in sour crude require special handling and treatment to mitigate the dangers associated with this gas, including corrosion of equipment and potential exposure to workers.

Other substances like methane, benzene, and carbon dioxide are present in crude oil to varying degrees but are not specifically indicative of "sour" crude. Methane is a natural gas component, benzene is an aromatic compound found in many petroleum products but does not define sour crude, while carbon dioxide can be found in both sour and sweet crude oils without being a defining characteristic. Thus, the defining attribute of sour crude oil is indeed its high levels of hydrogen sulfide.