This should help: Types of crude oil Crude oil quality is...

This should help:
Types of crude oil Crude oil quality is measured in terms of density (light to heavy) and sulfur content (sweet to sour). Density is classified by the American Petroleum Institute (‘API’). API gravity is defined based on density at a temperature of 15.6 ºC. The higher the API gravity, the lighter the crude. Light crude generally has an API gravity of 38 degrees or more, and heavy crude an API gravity of 22 degrees or less. Crude with an API gravity between 22 and 38 degrees is generally referred as medium crude. Sweet crude is commonly defined as oil with a sulfur content of less than 0.5%, while sour crude has a sulfur content of greater than 0.5%. Brent Blend Brent Blend is a light, sweet North Sea crude with an API gravity of approximately 38 and a sulfur content of approximately 0.4%. Most Brent Blend is refined in Northwestern Europe, but significant volumes are also shipped to the US and Mediterranean countries. Brent Blend is used for pricing around two-thirds of the crude traded internationally. Rolling price assessments are based on physical Brent-Forties-Oseberg crude oil cargoes loading not less than 10 days ahead and loaded free on board at the named port of shipment (‘Brent Dated).