Oil is classified according to three main categories: the geographic location where it was drilled, its sulfur content, and its API gravity (a measure of density). Oil is drilled all over the world. However, there are three primary sources of crude oil that set reference points for ranking and pricing other oil supplies: Brent Crude, West Texas Intermediate, and Dubai and Oman. Brent Crude is a mixture that comes from 15 different oil fields between Scotland and Norway in the North Sea. These fields supply oil to most of Europe. West Texas Intermediate (WTI) is a lighter oil that is produced mostly in the U.S. state of Texas. It is ―sweet‖ and ―light‖—considered very high quality. WTI supplies much of North America with oil. Dubai crude, also known as Fateh or Dubai-Oman crude, is a light, sour oil that is produced in Dubai, part of the United Arab Emirates. The nearby country of Oman has recently begun producing oil. Dubai and Oman crudes are used as a reference point for pricing Persian Gulf

oils that are mostly exported to Asia. The OPEC Reference Basket is another important oil source. OPEC is the Organization of Petroleum Exporting Countries. The OPEC Reference Basket is the average price of petroleum from OPEC’s 12 member countries: Algeria, Angola, Ecuador, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela. Sulfur is considered an ―impurity‖ in petroleum. Sulfur in crude oil can corrode metal in the refining process and contribute to air pollution. Petroleum with more than 0.5% sulfur is called ―sour,‖ while petroleum with less than 0.5% sulfur is ―sweet.‖ Sweet oil is usually much more valuable than sour because it does not require as much refining and is less harmful to the environment. Light oils are preferred because they have a higher yield of hydrocarbons. Heavier oils have greater concentrations of metals and sulfur, and require more refining.