Oils used by consumers are highly refined products that offer up key benefits to their application. We often hear of specially formulated additives added to base oils that allow them to stand out amongst other lubricators. While additives play a significant role in an oil’s unique performing properties, let’s take a step back and understand base oils and their types. 

Base oils can be labeled into 5 different types categorized Petroleum Base Oils and Synthetic Base Oils. Conveniently, the five types of oils are easily labeled from 1 to 5 in roman numerals for easy reference. 

Petroleum Base Oil

Group I

Group I base oils sit at the bottom of the rung as the least refined base oil. They undergo the least amount of processing from crude oil in the form of solvent refining and nothing more. As a result, it is the most affordable base oil available and is generally used for high oil consumption applications. Key values to identify a Group I base oil is a composition of less than 90% saturates and/or greater than 0.03% sulfur. 

Group II

Moving up, Group II oils go through solvent refining followed by hydrocracking. The second process purifies the oil further to offer better antioxidation properties over Group I base oils. Group II oils have notable performance in volatility, oxidation, wear prevention, and flash point. Group II is the most commonly used oil as it meets widely accepted consumer requirements. Its composition of saturates must be more than 90% with less than 0.03% sulfur and a viscosity index between 80 – 120 to be classified as a Group II oil.

Group III

Group III oils adhere to the same requirements as Group II oils but must have a viscosity index greater than 120. Treatment-wise, the Group III oils go through severe hydrocracking, hydro isomerized, and hydro treatment to be created. These extensive treatments allow it to have superior stability and molecular uniformity, taking Group III into synthetic lubricant levels yet categorized as a semi-synthetic oil.

Synthetic Base Oil

Group IV

The first of the synthetic base oils is not extracted from crude oil unlike the 3 before, but rather made from small uniform molecules that allow it to have predictable properties. Including extreme temperature stability, and tough condition performance assurance, the yielded product works efficiently in cold and hot climates alike. Identifying Group IV over the others is the presence of polyalphaolefins (PAOs) as a new element and a viscosity index of 125-200. 

Group V

The easiest oil to categorize is Group V. They are simply base oils that do not fall in the classification of Group I – IV. Commonly, this group has various esters and can be used in biodegradable base stocks and food-grade lubricants.