Sour crude describes crude oil containing relatively high levels of hydrogen sulfide and other sulfur compounds.
The word “sour” refers to sulfur content, not taste or acidity. Crude oil with comparatively low sulfur content is called sweet crude. Sour crude requires additional handling and refining because hydrogen sulfide is toxic, corrosive, and potentially flammable.
Refineries can process sour crude, but they generally need equipment and operating procedures designed for sulfur removal. Hydrodesulfurization uses hydrogen and catalysts to convert sulfur compounds into hydrogen sulfide, which can then be treated, commonly in a sulfur-recovery unit.
Sourness is separate from API gravity. API gravity describes whether a petroleum liquid is relatively light or heavy, while sulfur content describes a different chemical characteristic. Therefore, a crude can be light and sour, or heavy and sweet. These properties influence refinery configuration, processing cost, product yields, and the commercial value of a crude stream.