Base Oils

Base Oils

Lubricants have been around since ancient times. The Petroleum-based Lubricants business started in mid 1800’s. The initial processing was limited to separation by boiling point.  Most people know the key driver of the production for lubricants are Base Oils.

Here you will read about the different types of Base Oils, followed by a short overview of the base oil production and finally a few basic terms used in the Base Oil Market.

Mineral Base Oil

Modern mineral base oils are the result of a long and complex distillation and refining processes. The feedstock used is crude oil. This substance is not of uniform quality but consists of several thousands of hydrocarbon compounds in which the elements carbon and hydrogen are present in all molecules and, in part, are bound to other elements.

The hydrocarbons can be divided into three main groups: paraffinic, naphthenic and aromatic.

Paraffinic hydrocarbons can be further divided into two subgroups: normal paraffinic and isoparaffinic. Paraffinic hydrocarbons are the best lubricants. The distillation process in the refinery separates the hydrocarbons contained in the crude into cuts based on the molecule size.

Furthermore, as many unwanted substances as possible are removed in the process, such as sulphur, aromatic hydrocarbons, paraffin wax, etc. In other words the mineral oil production process is physical cleaning and the end product is so-called paraffinic base oil.

Most of the hydrocarbons in the base oil are paraffinic, but it also contains naphthenic and aromatic molecules. When the finished lubricant, such as motor oil, is made of these, several additive compounds are used to improve the base oil properties.

The final outcome can also be so-called naphthenic base oil, where most of the hydrocarbons are naphthenic. Their cold properties are excellent.

EHVI and VHVI base oils

VHVI (Very High Viscosity Index) oil, produced from crude oil using special processes, can be made to have properties close to those of synthetic oils. Raw material of the VHVI base oil is paraffinic hydrocracking fraction which is improved by removing waxes using the solvent extraction method.

The use of these base oils as components of modern motor oils is increasing, due to engine constructions that are more demanding in terms of lower emission properties and the new quality requirements of vehicle manufacturers.

Synthetic Base Oil

The group of synthetic base oils covers many different substances: synthetic hydrocarbons, organic esters, polyalkyline glycols, etc. Common to synthetic base oils is their production by a chemical process.

Synthetic PAO (Polyalphaolefine) hydrocarbons are manufactured in a process that results in isoparaffins, the desired types of hydrocarbon molecules. The raw material used is reprocessed into ethene gas (C2H4).

It is thus possible to produce the best possible lubricating oil, which entirely lacks the unwanted components, through chemical processes. This is the most commonly used synthetic base oil in modern engine lubricants.


At the production stage, the base oils for lubricants have gone through many quality-improving and cleaning stages that contribute to the properties required in future use. Additives can also improve the oil's cold properties, viscosity index and oxidation resistance, to enhance corrosion, pressure and wear resistance, and to prevent foaming.

In addition, the cleaning additives used in modern engine oils keep the pistons and inner parts of the engine clean of carbon and sludge deposits that tend to form impurities and high operating temperatures.

Base Oil Market selection:

As you understand from the above article there are different kind of Base Oils. Base Oil Market will focus on the five types of Base Oil according to API (American Petroleum Institute)



Viscosity Index


Sulphur in %




< 90%

> 0.03%

Conventional (Solvents)




≥ 90%

≤ 0.03%

Requires Hydroprocessing



≥ 90%

≤ 0.03%

Requires severe Hydroprocessing, often special feedstocks





PolyAlphaOlefins (PAO)






All other basestocks not in Group I – IV including other synthetics

Note that the base oil group category is followed by the manufacturing method (in bold print) and then a description of the oil characteristics for each category.

Group I - Solvent Freezing: Group 1 base oils are the least refined of all the groups. They are usually a mix of different hydrocarbon chains with little or no uniformity. While some automotive oils on the market use Group I stocks, they are generally used in less demanding applications.

Group II - Hydro processing and Refining: Group II base oils are common in mineral based motor oils currently available on the market. They have fair to good performance in lubricating properties such as volatility, oxidative stability and flash/fire points. They have only fair performance in areas such as pour point, cold crank viscosity and extreme pressure wear.

Group – III Hydro processing and Refining: Group III base oils are subjected to the highest level of mineral oil refining of the base oil groups. Although they are not chemically engineered, they offer good performance in a wide range of attributes as well as good molecular uniformity and stability. They are commonly mixed with additives and marketed as synthetic or semi-synthetic products. Group III base oils have become more common in America in the last decade.

Group IV -Chemical Reactions: Group IV base oils are chemically engineered synthetic base stocks. Polyalphaolefins (PAO's) are a common example of a synthetic base stock. Synthetics, when combined with additives, offer excellent performance over a wide range of lubricating properties. They have very stable chemical compositions and highly uniform molecular chains. Group IV base oils are becoming more common in synthetic and synthetic-blend products for automotive and industrial applications.

Group V - As Indicated: Group V base oils are used primarily in the creation of oil additives. Esters and polyolesters are both common Group V base oils used in the formulation of oil additives. Group V oils are generally not used as base oils themselves, but add beneficial properties to other base oils. Some examples of Group V Base Oils are: Alkylated Naphthalene, Esters, Poly-alkylene glycols, Silcones, Polybutenes.

Basic Concepts of Base Oils

Base stocks

Are called by several names: Neutrals (100N, 150N, 600N, …), Bright Stocks, Grades (SAE 5, 10…; ISO 22, 32..). The most common names are for group I (SN: Solvent Neutral), for group II (N: Neutrals) and group III grade names refer to the viscosity (4cst, 6cst, 8cst …). Grade names can also refer to trademarks.

Please note below example:





















Base Oil Production

The quality of Base Oil has evolved with the process technology. The first generation of process technology was developed to remove aromatics and other impurities. With the Solvent Processing Technology, it was possible to recover wax as a byproduct and lower the pourpoint and the simply hydrofining also added to the further reduction of impurities. In third phase the Hydroprocessing Technology was developed and this changed the base oil business from “Physical separations” to “Chemical transformations”. The technology could produce lighter viscosity grades, which was a popular option for the refineries. Some refineries use also Wax Isomeration to produce very high quality base oils.

In a nutshell the base oil production process works as follows:

  1. Feedstock is separated into distillates and vacuum gas oils
  2. Waxy vacuum gas oil molecules flow to the hydrocracker to begin conversion
  3. Hydrogen is introduced to saturate the molecules and remove impurities such as nitrogen, sulfur, oxygen and heavy metals.
  4. Hydrocracking, under conditions of extreme temperature and pressure in the presence of a catalyst, converts aromatics molecules into saturated paraffins.
  5. The altered stock is noticeably lighter in color due to the absence of contaminants.
  6. Long waxy paraffin molecules are restructured into shorter, branched isoparaffins that resist gelling and improve low temperature pumpability.
  7. Hydrogen is introduced again to remove any remaining aromatics and
    impurities, enhancing the oxidation and thermal stability of the now colorles oil.


Density means the volume weight of a substance. In oils, it is usually indicated in the temperature of +15°C or +20°C, in units kg/m3. Lubricant densities range between about 700 and 950 kg/m3, depending on the quality, viscosity and additive content of the lubricant.


The thicker a fluid is, the greater its viscosity. Nowadays, lubricant viscosity is usually expressed with the units centistoke (mm2/s) and centipoise (mPas).

Centistoke (cSt)
Centistoke is a unit of kinematic viscosity, based on the amount of force required to beat the internal friction of fluid.
Centipoise (cP)

Centipoise is a unit of dynamic viscosity, often used for expressing the internal friction of oil in low temperatures. The connection of cSt and cP is cP = cSt x fluid density. The temperature must always be given when expressing viscosity with any unit. All oils become much thinner as the temperature rises. A typical viscosity of motor oil SAE 10W at a temperature of -20 °C may be 2,000 cP, but if it heats up to a temperature of +100 °C the viscosity is only 5.2 cSt. Kinematic viscosity is measured by the pictured Ubbelohde viscometer. It measures the time the oil requires to flow from point m1 to point m2.

Viscosity index

Viscosity index (V.I.) describes the fluid’s tendency to thin as the temperature rises. The stronger the fluid thinning the smaller the viscosity index. The V.I. of single-grade motor oils is about 95-110, and that of multi-grade motor oils even higher than 200.

Flash point

The flash point expresses the flammability of a fluid. Flash point is the temperature at which, measured from the fluid with a certain method, flammable gases are vaporized so much that they flame up when ignited with a naked flame, but the fluid does not carry on burning.

Pour point

Oil thickens as the temperature falls. At a certain temperature it no longer flows by its own weight. This temperature is called the pour point. The pour point depends on, e.g., the viscosity and chemical structure of the oil. In paraffinic oils, stiffening is caused by the wax in the oil, which is distinguishable as crystals. The more the oil cools down the bigger the crystals grow, eventually forming a flow-preventing network within the oil.

Naphthenic oils have less or no wax, and they remain fluid in lower temperatures than paraffinic oils. The oil eventually becomes so stiff that it no longer flows with its own weight. Fully synthetic oils do not contain wax and their cold properties are excellent.

The pour point can be improved by using an additive that prevents the growth and interconnection of wax crystals. With the pour point, it is possible to describe approximately the cold start properties of oil, but in many cases it is not enough; it is more important to know the true oil viscosity at the starting temperature.