The Basics Of Base Oil

When talking about lubricant basics, base oils are the logical beginning point. All lubricants come with a base oil. Counting 70-95% of a lubricant’s composition, and these oils are considered their main elements.

Base oil is not found in nature but is refined from crude oil. Generally, about 2% of all crude oil created worldwide is used to make lubricants. However, you must take a few steps to make base oil from crude oil.

It acts as a base for lubricant oils before being mixed with additives or thickeners. But how can you understand which base oil is best? Well, in this article, you can learn the basics, categories, and base oil groups. And then you can know which base oil is best for you.

base oil groups

What Is Base Oil?

By refining crude oil, you can make the base oils. Basically, it means the crude oil is heated to separate the many distillates from each other. During the heating process, you can separate portable and weighty hydrocarbons.

The light ones are refined to produce gasoline and other fuels. Alternatively, the heavy ones are perfect for base oils and bitumen. Mainly one of the most common types is paraffinic crude oil. But naphthenic natural oils produce products with suitable properties and solubility at low temperatures.

By using hydrogenation technology, you can get highly pure base oil. Additives are chemical substances added to the base oil to fulfill the final product requirements. For example, the properties are cleaning and friction. Particular types of engine oil have more than 20% additives. On the other hand, do you want to know the base oil price? Well, it depends on the Group of base oils & regularly fluctuates depending on global conditions. For example, after the COVID-19 & Ukraine wars current base oil price is high which is almost 120-150 USD Per barrel.

What Is Base Oil Used For?

You need to use base oil to produce manufacturer products like motor oil, lubricating grease, and metal processing fluid. Different products require different compositions and properties in the oil.

One of the most important reasons is the liquid’s viscosity at various temperatures. The base oil molecules determine whether crude oil is perfect for making into a base oil.

Properties Of Base Oils:

Base oils usually have four properties that indicate how they operate in service:

Pour Point

The base oil sample will be determined with pour points at the lowest temperature.


Oil viscosity defines its resistance to flow. For example, honey is denser than water.

Viscosity Index (VI)

As oil temperature changes, viscosity also changes, and it is defined by the Viscosity Index (VI). A high-VI oil changes less viscosity with temperature than a low-VI oil. But chemically it is also possible to increase VI by using Viscosity Index Improvers!

Multi-grade motor oils specified by car manufacturers need high-VI as the starting point of the formulation process. High-VI oils have low volatility and come to work at high and low temperatures.


You should keep many lubricants like nitrogen, sulfur, and polycyclic aromatic compounds within strict limits.

Types of Base Oil

The three types of base oils are mineral, synthetic, and vegetable. Typically, mineral oil comes from refined petroleum, and its quality depends on refining.

Synthetic oils are artificial oils that can be useful in severe conditions. Lubricants for use on the human body can be oil, water, or silicone-based.

The American Petroleum Institute has five base oil titles. The first three groups evolved from mineral oil; Group IV base oils are synthetic. Group V is for all base oils, not only in Groups I to IV.

Group I

Group I base oils are lower than 90% saturated, more than 0.03% sulfur, and have an SAE 80-120 viscosity index range.

Besides this, its operating temperature range is 32 to 150 F. Moreover, it’s solvent-refined. That’s why it has a normal refining process, making the cheap base oil on the market.

Group II

Group II base oils are indicated as having more than 90% saturates, a V.I., and less than 0.03% sulfur. In addition, these oils come from hydrocracking.

Most importantly, it’s a complex process from solvent-refining. Furthermore, Group II oils come with excellent antioxidant characteristics. Also, it comes with a more transparent color than other base oils.

Group III

These are high viscosity index & low Sulphur content base oils. Group III base are used to produce high-performance engine oils, especially for long drain intervals giving automotive oils.

Its viscosity index is greater than or equal to 120″. Generally speaking, you can describe them as synthetic oils or hydro-cracked oils. In other words, few oil companies call their products synthetic oils.

Group IV

These base oils are called polyalphaolefins (PAOs). They are synthetic and produced through a process called synthesizing. PAO oils have a wide temperature range. Therefore, they are excellent for use in applications exposed to the utmost cold or high heat.

Group V

All the other base oils that don’t fall into different groups are classified as Group V. Examples include phosphate esters, silicones, polyol esters, polyalkylene glycols, and bio lubes. You can mix these oils with other base stocks to increase the properties of the oil.

Depending on structures, you can classify these types: naphthenic, paraffinic, and aromatic.

Check: Group 3 vs. Group 4 Oil

base oil groups

Importance Of Base Oil On Gear Oils:

Accordingly, you know that gear oils come from base oil. Here we have described some gear oils that come from vase oils. Have a look:

75W-90 Gear Oil

75W-90 is synthetic gear oil formulated from base oil and a developed additive system. Usually, it comes for use in railway gearboxes. More importantly, it provides excellent load-carrying capacity where extreme stress and shock loading can happen.

 Furthermore, it gives impressive oxidation, low pour point, thermal stability, and high-viscosity index. Consequently, this gear oil meets the API GL-5 performance level.

Features and Benefits

Gear oil comes to designs of Railway gearboxes and enhances the requirement for liquids. Notably, it provides higher performance with potentially increased productivity and lower operating costs.

Hypoid Gear Oils

Regardless, you can find these Hypoid gear oils in axle differentials. Therefore, to transmit energy from the driveline to the axle shaft, you can use it. These oils are mainly spiral bevel gears where the pinion is below the ring gear centerline.

Subsequently, they lower the driveshaft away from the bottom of the car. Hypoid Gear Oil comes with severe pressure (E.P.) additives to effectively protect and work Hypoid gears.

SAE 90 Gear Oil

SAE 90 gear oil is heavy-duty oil. Surprisingly, it comes with high-pressure antifoam and rust-proof additive oil. In general, it also provides anti-wear protection, which can decrease operating noise.

You can get from this oil a stable viscosity and oil seal. In the worst case, you can get extreme protection from this oil.


In short, you can use it in agricultural machinery, trucks, differentials, and extreme pressure types required for industrial reduction gears.

Final Word

To conclude, base oil offers a significant performance properties portion of end oil formulation. Choosing the proper base oil type is essential to developing an oil. Appropriate base oils keep metal parts lubricated and tools operating optimally.

Base oils are only the oil composition part. Engineers and scientists must also consider the implications of additive technologies. The actual performance of any lubricant is a combination of additives, base oil, and formulation for the application.


I am Engr. Z Eusuf Lubricant Specialist, Mechanical Engineer & has been working with engine lubricants for a long time and knows what makes them work best. I can help you find the right oil for your needs, and I have tips on how to keep your engine running at its best.

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