Do you really know what the 5 API base oil groups are?

Before additives are added, lubricating oils usually begin as one or more of the five API base oil groups. The base oil definition is: “oil with a boiling point range between 290 and 560 C, consisting of hydrocarbons with 18 to 40 carbon atoms.” This oil can be either paraffinic or napthenic in nature depending on the chemical structure of the molecules. Or the base oil can be fully synthesized from chemicals. The American Petroleum Institute (API) categorizes these base oils under one of 5 API base oil groups. The first three categories are
base oils refined from petroleum crude oil. Group IV base oils are full synthetic (polyalphaolefin) oils and Group V is for all other base oils not included in Groups I through IV.

Group I of the 5 API base oil groups.

Group I base stocks contain less than 90 percent saturates and/or greater than .03 percent sulfur and have viscosity index greater than or equal to 80 and less than 120.

These oils are meant to operate in a temperature range from 0 to 65 degrees C. Group I base oils are solvent-refined, which is a basic refining process. This is why they are the cheapest base oils on the market.

Definition of the Group II API base oil group.

This API base oil group has base stock that contains greater than or equal to 90 percent saturates and less than or equal to .03 percent sulfur and have viscosity index greater than or equal to 80 and less than 120. The refining process with these oils is more complex than what is used for Group I base oils: They are often manufactured by hydrocracking.

Group II base oils have better antioxidation properties because all the hydrocarbon molecules of these oils are saturated. They also have a clearer colour and are more expensive when compared to Group I base oils. Because of the higher operational demands on modern lubricants Group II base oils are becoming very common in the base oil market today, with the pricing very close to Group I oils.

Group III base stocks are a highly refined API base oil group.

Group III base stocks contain greater than or equal to 90 percent saturates and less than or equal to .03 percent sulfur and have viscosity index greater than or equal to 120.

Group III base oils are refined even more than the Group II API base oil group and are generally severely hydrocracked (higher pressure and heat). This process results in a purer base oil with less contaminants, such as sulphur and paraffin. Whilst being made from crude oil, Group III base oils are sometimes described as synthesized hydrocarbons, which unfortunately confuses the consumer wishing to buy a full-synthetic oil. Much like Group II base oils, these oils are also becoming more prevalent in industrial use.

The Group IV API base oil group is for true synthetic base stock.

Group IV base stocks are polyalphaolefins (PAO). These oils are true synthetic lubricants, made through a process called synthesizing. They have a much broader temperature range and are great for use in extreme cold conditions and high heat applications. They also have higher shear strength, and are less prone to oxidation at higher operating temperatures.

Although a little more expensive than the crude API base oil groups, synthetic lubricants have extended life and don’t degrade as rapidly as regular oils, thereby saving on oil changes downtime. They are also more energy efficient, resulting in further operating cost savings.

Group V covers all base stocks not in the first 4 API base oil groups.

Group V base stocks include all other base stocks not included in the I, II, III, IV API base oil groups. These include silicone, phosphate ester, polyalkylene glycol (PAG), polyolester, biolubes, etc. Sometimes these base oils are mixed with other base stocks to enhance the lubricant’s properties.

An example of this would be a PAO-based compressor oil that is mixed with a polyolester. Esters are Group V base oils commonly used in different lubricant formulations to improve the properties of the other base oil. Ester oils can operate at higher temperatures whilst also providing superior detergency compared to PAO synthetic base oils. This improves their oxidation resistance which in turn increases the oil change intervals.

Typically, only between 1% to 2% of a barrel of crude oil is refined into base oil. The majority of the barrel is used to produce gasoline and other hydrocarbons.

Lubricating oil is produced by "Blenders and Compounders" who combine base oil with 1% to 20% application-specific chemical additives, which enhance the performance of the base oil. The "compounded" Lubricating oil is then packaged and sold to end users.

To meet the exacting demands of expensive equipment it’s important that a lubricant from the correct API base oil group is selected. The professionals at Habot Synthetic Lubricants have a wide range of quality synthetic oils that will meet or exceed your requirements.