Sulfur is an element commonly found in crude oil and petroleum products. Sulfur is considered an undesirable contaminant because, when burned, it generates sulfur oxides. Consequently, most finished petroleum products have a limit on how much sulfur they can contain, making sulfur removal an important part of the overall refinery process. Sulfur can also harm some of the catalysts used in refining process units so it must be removed from some intermediate streams before they can be fed to a conversion unit.

Once separated, sulfur can be sold as a low-value finished product, either as solid sulfur or in a molten state. The major use for sulfur is in the petrochemicals industry.

As a general rule, a crude oil grade with high sulfur content will have a lower value. This type of crude is often referred to as a sour crude.

Most of the sulfur in crude oil is removed during processing. Some of it is removed in conversion processes as hydrocarbon molecules that containing sulfur are cracked and form H2S. Sulfur is also removed directly from processing a hydrocarbon stream through hydrotreating, where the sulfur in the hydrocarbon is replaced with a hydrogen atom, and the released sulfur is combined with two free hydrogens to form H2S gas.

H2S gas is typically collected from the various conversion and hydrotreating units and converted into elemental sulfur in a sulfur plant. Some refineries will further process the sulfur to sulfuric acid.