Extracted in its natural unrefined state from the ground, crude oil significantly varies in its consistency and density – from a volatile and relatively thin liquid to a semi-solid and viscous substance. Still, often referred to as the ‘black gold’, the color of different crude oils may also vary from a light, golden yellow to dark black.

3 factors of crude oil classification

·         Viscosity defines the ability of oils to flow. Higher viscosity makes oil more difficult to flow. As such, it takes much energy to pump it from the ground.

·         Volatility defines the speed of oil evaporation. Higher volatility requires additional measures to monitor the environment during the extraction process to make sure only the smallest part of oil is lost due to evaporation.

·         Toxicity defines the poisonous and harmful effects of oil on the environment, people and wildlife during the production and refinement process. In case of oil spills, which have happened occasionally throughout the history of oil transportation, each oil type requires different measures to minimise any potential hazard.

4 major types of crude oil

The four principal types of oil are:

1.     Very light oil

This type tends to be very volatile, evaporating in just a few days, which makes it less toxic.

Very light oil is mainly used in the following crude oil products: gasoline, jet fuel, petroleum spirit, kerosene, petroleum ether and petroleum naphtha.

2.     Light oil

This type is moderately toxic and volatile. It is mainly used for the following crude oil products: fuel oils (grade 1 and grade 2), diesel fuel oil and domestic fuel oils.

3.     Medium oil

The most common type of oil with low volatility and higher viscosity, which makes it more toxic and potentially more hazardous and challenging during occasional cleanups.

4.     Heavy fuel oil

The least volatile, the most toxic and viscous type of oil.

It is mainly used for the following crude oil products: the heaviest 3, 4, 5 and 6 fuel oils and heavy marine fuel.