Base Oil is the name given to lubrication grade oils initially produced from refining crude oil (mineral base oil) or through chemical synthesis (synthetic base oil).

Base oil types generally are as below:

Mineral/Petroleum Base Oils

The mineral base oil can be obtained by means of refining crude oil. A little portion of the crude oil, about 1 to 2% of a crude oil barrel is subjected to be refined to produce base oil. 

Group 1

Group I base oils are classified as less than 90 percent saturates, greater than 0.03 percent sulfur and with a viscosity-index range of 80 to 120. The temperature range for these oils is from 32 to 150 degrees F. Group I base oils are solvent-refined, which is a simpler refining process. This is why they are the cheapest base oils on the market.

Group 2

Group II base oils are defined as being more than 90 percent saturates, less than 0.03 percent sulfur and with a viscosity index of 80 to 120. They are often manufactured by hydrocracking, which is a more complex process than what is used for Group I base oils. They have a clearer color and cost more in comparison to Group 1 base oils. Still, Group 2 base oils are becoming very common on the market today and are priced very close to Group I oils.

Group 3

Group III base oils are greater than 90 percent saturates, less than 0.03 percent sulfur and have a viscosity index above 120. These oils are refined even more than Group 2 base oils and generally are severely hydrocracked (higher pressure and heat). Group 3 is also known as synthetic technology oils or hydrocracked synthetic oils.

Synthetic Base Oils

The synthetic base oil is manufactured through chemical synthesis. This product is sorted into paraffinic and naphthenic types based on the chemical structure of the molecules.

The base oils have been categorized into five categories. The first three groups are refined from petroleum crude oil. Group IV base oils are full synthetic oils. Group V is for all other base oils not included in Groups I through IV.

Group 4

Group IV base oils consists of synthetic oils which are made of Poly Alpha Olefins (PAO). PAO Oils are much more stable in various temperatures compared to others. PAO oils are highly recommended for being used in freezing areas as in Northern Europe as well as hot areas as in the Middle East since they have a much broader temperature range and are great for use in extreme cold conditions and high heat applications.

Group 5

Group V base oils is devoted to naphthenic oils and esters. Esters are common Group V base oils used in different lubricant formulations to improve the properties of the existing base oil. Ester oils can take more abuse at higher temperatures and will provide superior detergency compared to a PAO synthetic base oil, which in turn increases the hours of use.

Base oils are also classified according to their viscosity index to whether they are Low Viscosity Index (LVIs) or Medium Viscosity Index (MVIs), High Viscosity Index (HVIs) or extra High Viscosity Index (XHVIs). As a general notion, the more viscosity index is, the darker the color will be.

Grades of base oil

There are different grades of base oil group 1 which has different properties:

Base Oil SN650

Base Oil SN350

Base Oil SN 150

Base Oil SN 300

Base Oil SN 500

SN stands for Solvent Neutral base oil and the numbers are based on the SUS (Saybolt Universal seconds)