The starting product for most lubricants and fuels is crude oil. The crude oil consists largely of hydrocarbons. When it is extracted, it is heavily contaminated with water, sulfur, nitrogen, oxygen, and with solid foreign matter or metallic elements. Depending on which part of the world the black gold comes from, the sulfur content can be less than 1% (10,000 mg/kg or ppm) or up to about 6% (60,000 ppm).
The removal of sulfur from crude oil is very costly in the refinery; consequently, finished products can be extracted from low-sulfur oil at lower cost. Thus, the sulfur content also affects the price of crude oil. Sulfur is bound in crude oil in various compound forms, such as hydrogen sulfide (H2S).
Too much sulfur in the base oil of lubricants can cause acid formation, among other things, which causes non-ferrous metal corrosion. To avoid this, the starting product must be desulfurized. In Germany, the maximum permissible sulfur content of some petroleum products, especially fuels, is prescribed by law.
For example, to reduce pollutant emissions, diesel fuel must not contain more than 10 ppm or 0.001% sulfur. Thanks to this regulation, environmental pollution from acid rain containing sulfuric acid has decreased dramatically.
However, the level of sulfur in the base oil used to produce an engine, gear or hydraulic oil depends on its geographic origin, the degree of desulfurization and, ultimately, the price paid for it. Even oils from the same producer and with identical product names can show significant base oil-related differences in sulfur content, especially if the oils are produced in different countries