Crude oil contains much more than just carbon and hydrogen; it also contains nitrogen, helium, and other gasses , as well as relatively small amounts of sulfur, heavy metals, and other impurities. Sulfur is by far the most important impurity segment in crude oil and can range from 0 percent to 6 percent or more.
API Gravity is a measurement developed by the America Petroleum Institute (API), which judges the “purity” of oil, or the degree to which is inundated with or devoid of sulfur. The measurement is a crucial factor in deciding the economic value of crude oil, and it has enormous implications on the oil refining process and other related areas.
High-gravity crudes, which are light compared to low gravity crudes, almost always contain less sulfur and less nitrogen than the lower gravity crudes. This this makes the refining process less expensive. In addition, higher gravity crudes contain more natural gasoline than lower gravity crudes, again making them easier to refine into gasoline. But because refiners are not always trying to make gasoline and because often it is necessary to mix crude oils in order for the refinery to work optimally, it is sometimes in a refiner's best interest to buy lower gravity crudes.
API gravities can range from the mid 70s to the teens, but values are most commonly in the 20s to 40s. This is the range in which most Middle Eastern oil is located.
- Low gravity (heavy oil), involves crude with a 20 API and lower, and are rich in sulfur.
- Medium gravity involves crude falling in the 21 API to 34 API range.
- High gravity (light oil) involves crude of 35 API and higher, and is low sulfur.
Crude oil that have a low sulfur content are referred to as "sweet" and those with a high content are referred to as "sour". If you smells high and low sulfur crude, you’ll understand why.
© 2000 Mena Report (www.menareport.com)
