In the petroleum industry, Low-Sulfur Oils are called Sweet Oils and High-Sulfur Oils are referred to as Sour Oils. The names come from the fact that oil which is low in Sulfur has a sweet taste and high Sulfur oil is bitter. The more Sulfur the Crude Oil contains, the less Energy it produces per gallon, barrel, or litre.

There are 3 main reasons that make High-Sulfur (Sour) crude oil a lower quality - therefore less expensive - than Low-Sulfur (Sweet) crude oils.

Reason #1

High-Sulfur crude oils produce much Greater Emissions, particularly the emissions that are toxic and have a high global warming potential. The Sulfur in Sour crude reacts to different components in the Air to produce toxic emissions like Sulfuric Acid and Nitric Oxides.

Reason # 2

High-Sulfur oils cause oxidation and corrosion. Because of its high oxidation and corrosion qualities, refining high-sulfur crude oil is more expensive. If a Refinery is not properly fitted to support high-sulfur crude oil - and is well maintained on a regular basis, - the oxidation and corrosion damage generated will eventually exceed the Profits.

Reason # 3

The higher the Sulfur count, the lower the hydrocarbon count. Hydrocarbons being the component in Petroleum that combusts and generates energy. Generally, Carbon and Hydrogen make up around 98 percent of the content of a typical crude oil type. The rest is made up of Sulfur (1-3 percent), nitrogen, oxygen, metal, and salts (less than 1 percent each).

To sum it up, the more Sulfur a Crude Oil contains, the fewer Hydrocarbons it contains on a volume scale.