Base Oil Groups: Understanding Properties and Applications

Jul 31, 2019 | Renkert News

Lubricants play an integral role in how our world functions. Automobile and truck engines the biggest consumers of lubricants worldwide, using 20 million tons per year, which means that motor oils often help to drive this industry. They’re also used in industrial applications, cooking, the medical field, and virtually any other sector you can imagine. Just about every lubricant begins as a base oil, which is typically produced during the crude oil refining process.

There are numerous types of premium base oils that you can obtain from base oil suppliers. But in order to determine which type of base oil will best suit your application, you’ll want to learn a bit more about what’s available to you. The American Petroleum Institute (or API) has categorized the different types of base oils into five distinctive groups. Understanding these class distinctions will prove essential when conducting business with base oil suppliers to choose the right product.

The characteristics of base oils that are used to determine their performance may include:

  • Pour point
  • Viscosity and viscosity index
  • Purity
  • Volatility
  • Thermal stability
  • Hydrolytic stability (water resistance)
  • Oxidation
  • Sulfur and saturate content

Group I

Generally speaking, Group I base oils are made using solvent extraction or solvent refining processes, which are meant to remove any undesirable aspects of the original oil. When you work with base oil plants to obtain products from this group, these oils will be classified as having less than 90% saturates and greater than 0.03% sulfur. Their viscosity index range will be anywhere from 80 to 120 and their temperature range extends from 32 to 150 degrees Fahrenheit. Although these are among the most affordable base oils available and make up the largest category in the global marketplace, the demand for these oils is on the decline. However, they are still readily used in certain engine oils, industrial applications, and marine lubricants.

Group II

Like Group I base oils, Group II base oils are considered to be mineral oils. They contain more than 90% saturates and less than 0.03% sulfur, while offering a viscosity index range of 80 to 120. They tend to have improved anti-oxidation properties, as compared to Group I oils. That said, they are more expensive and are manufactured in a more complex way (through a process called hydrocracking). But since the vast majority of lubricants used worldwide can be made from Group II base oils, it makes sense that this particular category is the most popular.

Group III

Considered by many to be the best grade of petroleum base oil, Group III oils contain greater than 90% saturates and less than 0.03% sulfur. One of the biggest differences is that their viscosity index range extends above 120. While they’re made in similar ways to Group I oils, Group III oil creation involves higher pressures and temperatures. As a result, these oils are purer and more desirable. Group III base oils are becoming more prevalent, particularly as automobile fuel economy increases in importance.

Group IV

Unlike the first three base oil categories, which are all mineral oils, Group IV base oils are polyalphaolefins — synthetic base oils that are created through a much different process (aptly called synthesizing). As your base oil supplier will tell you, this can be used to create products with wider temperature ranges and thermal stability in challenging conditions. In fact, their viscosity index ranges may reach 140. They also have improved oxidation stability. But while this is the most readily used type of synthetic base oil, it’s important to know that the solubility, lubricity, and strength of these oils can be a detriment. And because of cost and availability, they will never be as widely used as the mineral base oils outlined above.

Group V

This is the group with the most variety, as it’s the catch-all category for all other base oils (including polyesters, diesters, polyalkylene gycols, silicones, naphthenic oils, phosphate esters, biolubes, and more). Essentially, if the oil is synthetic and is not a polyalphaolefin, it’s classified as a Group V oil. In many cases, Group V oils are used as a supplement to other base oils, rather than being used as a base on their own.

As one of the leading base oil suppliers, we’re here to help you choose the right product for your application. To find out more, contact us today.