Classifications or Grades
Generally speaking, oil with an API gravity between 40 and 45 commands the highest prices. Above 45 degrees the molecular chains become shorter and less valuable to refineries.
Crude oil is classified as light, medium or heavy, according to its measured API gravity.
- Light crude oil is defined as having an API gravity higher than 31.1 °API (less than 870 kg/m3)
- Medium oil is defined as having an API gravity between 22.3 °API and 31.1 °API (870 to 920 kg/m3)
- Heavy crude oil is defined as having an API gravity below 22.3 °API (920 to 1000 kg/m3)
- Extra heavy oil is defined with API gravity below 10.0 °API (greater than 1000 kg/m3)
Not all parties use the same grading. The United States Geological Survey uses slightly different definitions.
Crude oil with API gravity less than 10 °API is referred to as extra heavy oil or bitumen. Bitumen derived from the oil sands deposits in the Alberta, Canada area has an API gravity of around 8 °API. It is "upgraded" to an API gravity of 31 °API to 33 °API, and the upgraded oil is known as synthetic crude.
Read more about this topic: API Gravity
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