Automotive Lubricants

Base Oils and Their Applications


Base Oils and Their Applications
© Jostaphot


Base oil is the beating heart of almost any lubricant. Here are some examples should there be any doubt. Engine oil contains about 7%-10% additive chemicals, but the rest is base oil. Transmission fluids contain a bit more additives—maybe 10%-12%; the rest is base oil. How about grease? An NLGI 2 grease contains about 90% base oil with the rest being made up of thickener and additives.

So the base oil is the predominant component, but the base oil quality and viscosity varies depending on the application and the environment in which the finished product is operating. Let’s take a look at the base oil for several applications, the desirable properties and how they are refined.

As I often do, I want to go back in history to help you understand how this all started. That reminds me of a line from the movie “Airplane,” in which Lloyd Bridges asks the tower controller to tell him everything. The controller, Stephen Stucker, says, “Well, in the beginning there were dinosaurs, and then….” In a sense, it did all start with dinosaurs.

The first actual oil-producing well was the one drilled by Colonel Drake in Bradford, Pennsylvania, in 1859. The search for kerosene was the impetus since sperm whale oil, which was used for lamps as fuel, was becoming scarce. The crude oil was simply separated to get the light ends, and the rest was left behind. Some entrepreneurs started selling it as a miracle healing salve, while others just used it to control dust on the road. However, there were some more reasoned approaches taken to see what could be done with the “bottoms.”

Today we can see that crude oil is a gold mine of materials used for many applications. Several hundred products that serve modern society are contained in or derived from crude oil. The table below provides an overview of the various products we take for granted every day.

Table 1. Petroleum Products Produced from One 42-gallon Barrel of Crude Oil
Source: U.S. Energy Information Administration
Finished motor gasoline19.40
Distillate fuel oil13.44
Kerosene-type jet fuel2.90
Petroleum coke2.18
Still gas1.76
Hydrocarbon gas liquids1.55
Asphalt and road oil0.92
Residual fuel oil0.55
Naphtha for feedstocks0.50
Other oils for feedstocks0.29
Miscellaneous products0.25
Special Naphthas0.08
Finished aviation gasoline0.04

If you look carefully, you will see that lubricants account for 0.42 gallons per barrel, or about 1%. That’s a testimony to how much crude is processed in North America because 279,000 barrels of base oil are produced daily in the United States, Mexico and Canada. The base oils here include naphthenics as well as Group I, II and III paraffinic base oils.

All base oil types have specific properties that make them valuable in certain applications. I want to take some more well-known applications and describe how the base oil choices make each product type successful. But first, let’s talk about how base oil is processed and what makes one type better than another.

Refining is, at its core, distillation of the crude oil. When it boils, the various products are separated by boiling range. The first distillation is at atmospheric pressure and tops out at about 700 degrees Fahrenheit. The materials produced are mostly solvents, chemical feedstocks, gasoline and diesel. What’s left is distilled again but this time under vacuum. This reduces the temperature at which the fractions are separated while minimizing cracking and oxidation. The results are heavy oils and waxes. The bottoms left from vacuum distillation are bright stock, asphalt and coker feed. The stream from vacuum distillation is the source for most base oils. This stream is either cut into various fractions when it is distilled or goes on to be further processed.

The base oil group system was developed in the early 1990s to define the quality of various processing schemes as it relates to engine oil development. It was created as part of the API 1509, Engine Oil Licensing and Certification System. Although not made for that purpose, the system has become a means of defining base oil quality in general.

Table 2. Base Oil Groups
Source: API
GroupViscosity IndexSulfur, wt%Saturates, %Description
I≥80 < 120> 0.03< 90Classic solvent refined base oil
II≥90 < 120≤ 0.03≥ 90Hydro-processed base oil
III≥ 120≤ 0.03≥ 90Severely hydro-processed base oil
VNANANAEverything else

Group I base oils are usually solvent extracted and dewaxed oils with viscosity indexes in the 80s, sulfur levels above 0.03% wt. and saturates less than 90%. The crude source makes a big difference in the type of Group I base stock produced. My experience with them includes a very naphthenic crude, which resulted in a 90N (very volatile), a 300N and a bright stock. I also worked with a more paraffinic crude, which produced a 100N, a mid-viscosity neutral and bright stock. In addition, there are such byproducts as lube extracts, waxes and asphalt.

Group II base oils are produced using hydrogen in a process called hydrogenation or hydrotreating. Group III base oils are made in much the same way as Group II mineral oils, except the hydrogenation process is coupled with high temperatures and high pressures. The cracked material is then separated into viscosity grades, dewaxed catalytically and finished with mild hydrotreating. The result is two or three viscosities of high VI (over 90 for Group II and 120 for Group III), virtually no sulfur (<0.03% wt) and saturates well into the 90%+ range. Because of the cracking process, no bright stock is produced and wax is relatively nonexistent. No extracts are produced, either. Group IV is reserved for polyalphaolefins, which are truly synthetic and are produced from a specific stream refined from crude.

Among the products in Group V are naphthenics. These base oils from naphthenic crudes are processed in various ways, including solvent treated and hydrotreated. There is no specific processing used or set limits on VI, sulfur or saturates. They are often distilled to various viscosity cuts without further treatment.

Group II base oils represent the majority of base oils refined in North America. The move to Group II was facilitated by the fact that a wider slate of crudes could be used and that there were less yield losses because the reduced crude was essentially “cleaned up” by the process. Less yield loss, wider crude slate processing and higher-quality finished product is a no brainer.

To a great extent, the properties of base oils dictate how they are used. In almost all cases, the finished products that are produced owe a lot to the additive technology that goes into any application. Additives typically improve the oil properties (e.g. pour point depressants), protect the base oil (e.g. antioxidants) or protect the lubricated surface (e.g. corrosion inhibitors).

Group II base oils represent the majority of base oils refined in North America. The move to Group II was facilitated by the fact that a wider slate of crudes could be used and that there were less yield losses because the reduced crude was essentially “cleaned up” by the process.

Base oils find most of their use in automotive products, including engine oils, transmission and gear lubricants, and greases. Other major uses are in process oils and general industrial lubricants.

Group I base oils are commonly used in industrial, grease and gear lubricants. Engine oils can be made successfully but require a more robust additive package due to the lower saturate levels and higher sulfur. They also make good metalworking fluids (in which oil-based products are needed or desired). They have good solvency properties as well, making them useful for certain specialized applications. They are the only source of bright stock, which is high-viscosity, thermally stable base oil. Bright stock has some unique applications in which the high-temperature thermal stability is important. Two-cycle engine oils are a good example.

Table 3. North American Base Oil Production
Source: Lubes’n’Greases research
Base Oil GroupBBL/Day
Group I62,500
Group II148,400
Group III5,900
Group V (Naphthenic)44,500

Group II base oils are widely used in modern engine oils and transmission fluids. The latest API category (SP/GF-6) is moving toward lower viscosities, which—along with volatility limitations—are pushing Group III and synthetic base oils into the new standard SAE 0W-20 and SAE 0W-30 engine oils. As far as transmission fluids are concerned, Group II and Group III or synthetic base oil blends are now the norm.

Group III base oils are used in superior quality engine oils, transmission fluids and certain industrial oils in which extreme stability, low viscosity and low volatility are required. They are mostly used as trimming base oils when a finished oil needs some help to reach low viscosity or volatility requirements. Their use will likely grow in the future.

Table 4. Lubricant Product Market Share
Source: Lubes’n’Greases research
Product Type% Share
Engine Oil49
Process Oil29
General Industrial Oil15
Gear & Transmission Oil9

Naphthenics are used in specialized applications when low pour point and good seal conditioning are at a premium. They are used in transformer oil in which their good dielectric properties are desired. They are also used in process oil applications calling for special mineral oil products to manufacture products in the chemical and technical industries.

So that’s the rundown on base oils. You can bet that they, or something very much like them, will be around and used for a very long time.  

Steve Swedberg is an industry consultant with over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at