Classification of oil

Petroleum classification is dependent on the intrinsic properties.  There are various categories which are related to the density (referred to as API° gravity), sulphur content, extraction process and geographical location.

The most common classification is

1.      Heavy oil

2.      Light oil

3.      Sour

4.      Sweet

Heavy oils imply that they have a low API° gravity whilst light oils have a high API° gravity implying that they flow easily, hence presenting fewer flow assurance challenges.

Sour or sweet are used to express the amount of sulphur. Oils with low Sulphur  amounts are referred to as sweet while petroleum with large amounts of Sulphur are referred to as sour. Crude oils that are light and sweet demand a higher price than heavy, sour crudes. They are more desirable because their processing is cheaper and less energy intensive. Furthermore, market demands for gasoline and diesel (which are typically sold at a significant premium) require low Sulphur content.

Some are classified as conventional or unconventional which implies the extraction process involved. Conventional oil is extracted from sub-surface reservoirs while non-conventional oil is derived from oil shales, tar sands and coal liquefaction.

There are multiple classifications that may be applied to crude oil depending on the physical or chemical properties, however of the above mentioned classifications, density (API° gravity) is the most common method.  In the crude oil market, density and Sulphur content are two of the most important characteristics.

Stay tuned for the next post on crude oil from different geographical regions.