The petrochemical industry classifies crude oil by the geographic location it is produced, its API gravity (an oil industry measure of density denoting the wax content of the oil), and by its sulfur content. light if it has low density or heavy if it has high density (higher specific gravity is better and lighter); sweet if it contains relatively little sulfur or sour if it contains higher amounts of sulfur.
Tracking geography is important since crude needs to be transported to the refinery. Light crude oil is more desirable than heavy oil since it produces a higher yield of gasoline, while sweet oil commands a higher price than sour oil because it has fewer environmental problems.
The reference crude oil grades that are commonly used are:
- Arab Light, light sour oil, produced by Saudi Arabia. While Saudi Arabia has multiple ports in Persian Gulf and the Red sea the most active port by throughput is the Kind Fahad Jubail Industrial Port that ships about 35 million tonnes of petrochemical cargo every year.
- West Texas Intermediate (WTI), a high-quality, sweet, light oil delivered at Cushing, Oklahoma for North American oil
- Brent Blend, comprising 15 oils from fields in the Brent and Ninian systems in the East Shetland Basin of the North Sea. The oil is landed at Sullom Voe terminal. Oil production from Europe, Africa and Middle Eastern oil flowing West tends to be priced off this oil, which forms a benchmark
- Dubai-Oman, used as benchmark for Middle East sour crude oil flowing to the Asia–Pacific region
- Tapis (from Malaysia, used as a reference for light Far East oil)
- Minas (from Indonesia, used as a reference for heavy Far East oil)
- The OPEC Reference Basket, a weighted average of oil blends from various OPEC (The Organization of the Petroleum Exporting Countries) countries