The American Petroleum Institute gravity, or API gravity, is a statistic that is used to compare a petroleum liquid's density to water. Light crude oil has an API on the higher side of the scale, while heavy oil has a reading that falls on the lower end of the range.Accordingly, crude oil is classified as light, medium, or heavy, according to its measured API gravity.
- Light Crude: API gravity > 31.1°API
- Medium Crude: API gravity between 22.3°API and 31.1°API
- Heavy Crude: API gravity < 22.3°API
How sweet a petroleum is depends on the sulfur content of the underlying fuel, with 0.5% being a key benchmark. When oil has a total sulfur level greater than half a percent, it is considered 'sour', while a content less than 0.5% indicates that an oil is 'sweet'.End users generally prefer sweet crude as it requires less processing in order to remove impurities than its sour counterpart. WTI and Brent are considered sweet crudes and come primarily from the Central U.S. and North Sea region respectively. Oman Crude mainly comes from the Middle East region and is considered less sweet compared to WTI and Brent. Sumatran Light, from the island of Sumatra, is a light, sweet crude. Tapis is of extremely high quality and very light and very sweet. It comes from a single field in Malaysia and at one time was referred to as the world's costliest oil. Bonny Light comes from Nigeria and is a light, sweet oil. Isthmus-34 Light is a sour crude produced in Mexico with an API gravity of 33.74 degrees and a sulfur content of 1.45%.