In the early 1990s, the American Petroleum Institute (API) produced a system to categorize the various types of Base Oils being produced. This organization listed 5 possible groups namely Group I, II, III, IV, and V. The most common group (Group I) was traditionally used throughout the industry and was known as “solvent refining” of crude oil. These refineries were built from 1940 until 1980.

Today’s modern equipment and lubrication requirements are constantly changing with the latest technological improvements and upgrades where more demanding parameters and lubrication specifications are of the utmost importance.

Almost all lubricants begin with a base oil of sorts prior to the addition of additives and performance-enhancing chemistry. These base oils may be selected using one group of base oils or a mixture of these groups, depending on the final product requirements.

Group I

This group is produced in designated refineries built for the sole purpose of producing group I base oils. Crude or fossil fuel undergoes both physical and mechanical processes to remove impurities such as aromatics, sulphur, water, salts, and wax to name a few. This form of refining is the simplest type of refining of crude and is therefore the most cost-effective form of base oil available. This group has a natural (VI) viscosity Index of between 80 – 120. This is known as a High Viscosity Index product.

Group II

Although this group is still extracted from crude or fossil fuel, they undergo a process known as “Hydrogen Finishing” or “Hydrotreating” to remove additional impurities from the product, producing a purer grade of base oil. In order to achieve this, hydrogen is chemically reacted with the crude oil to improve product cleanliness.

Group II is lighter in colour due to the additional removal of sulphur and other impurities. This group also possess better antioxidation and corrosion prevention characteristics as well as a naturally higher (VI) Viscosity Index stability. The viscosity Index ranges between 80 – 120. Recent pricing indications show that group II base oils are becoming more price competitive and are now almost in line with group I.

Group III

This group is once again further refined in comparison to both Group I and II, is still produced from crude oil, and is clear or “water white” in colour. These products are produced under higher temperatures and pressures, a procedure which is known as “Hydrocracking”. This extended procedure is designed to produce a purer base oil in comparison to the two previous groups.

They are also known as synthesized hydrocarbons and are substantially more expensive than the previous groups mentioned. This group also boasts a natural VI of in excess of 120.

Group IV

These base oils are further refined and make use of polyalphaolefins (PAOs) and are manufactured through a process called synthesizing.

Group V

Includes any other base oil type including silicone, polyester, phosphate ester, polyalkylene glycol (PAG) plus various other elements.  These groups of base oils and their applications will be discussed in a later blog.

Some positive and negative influences of using either Group I, II or III

Price

Although group II pricing is now becoming more affordable, the cost of this product has been generally higher than group I products. The pricing of group III has increased substantially due to supply and demand as well as world economical hurdles such as the Ukrainian invasion by Russia.

Viscosity Index

The natural VI (Viscosity Index) of both group II and III base oils ranges from 105 to over 120, which is a positive characteristic as it is higher compared to that of group I whose VI is around 100. The benefits relative to this include improved lubrication at elevated and lower operating temperatures and the amount of Viscosity Index Improver (VII) required to meet certain finished lubricant requirements.

Aromatic Content

The lower aromatic content produced in the manufacture of group II and III base oils allows for higher thermal ability and lower volatility of the finished product. These product groups are, therefore, highly recommended for the formulation of today’s high-performance automotive engine oils.

Sulphur Content

With regards to the natural sulphur contents of the three groups discussed, group I contains more than 0,03% sulphur, whilst group II and III less than 0,03% sulphur.

The lower the sulphur, the better the ability to improve the anti-oxidation and anti-corrosion characteristics of a lubricant. Additionally, the low sulphur content of the base oil will also have a positive influence on applications where yellow metals (copper, brass, bronze etc.) may be present in certain lubrication applications.

Taking the above into account, certain lubricants including automotive and industrial gear oils require high levels of sulphur content to produce extreme pressure (EP) characteristics. This is achieved by adding sulfurized additives to the finished product formulation.

Colour

The lighter colour of both group II and III base oils compared to the equivalent viscosity grades produced by group I refineries, differ substantially.

On occasions, lubricant users have the perceived idea that these lighter-coloured products don’t contain the required additive package and therefore don’t meet the specifications or that the product is inferior. The transfer of knowledge to the consumer in this regard is paramount.

The mixing of groups I, II and III are not uncommon, dependent on the product being formulated. It must be kept in mind that the purity of the base oils mixed may jeopardize the final product once manufactured.

Another major reason for the increased usage of group II base oils may be due to natural disasters such as hurricane Katrina in August 2005 which besides costing over 1,800 lives, and billions of dollars in damages, many group I oil refineries – particularly on the Gulf of Mexico – were completely destroyed or severely damaged and weren’t rebuilt to produce group I base oils.

New refineries built were to manufacture group II base oils.

The invasion of Ukraine by Russia in February 2022, may also, in future, upset the apple cart where base oils are concerned.

Finally, other difficulties which may be encountered could be that due to the low aromatics present in the group II base oils, formulators and blenders may on occasion have difficulty in forming stable formulations which may “split” or separate when mixed with other products and certain additives.

The discussion of the various types or groups of base oils is a vast subject and open to many individual ideas, recommendations, and suggestions. However, should you have any additional questions, do not hesitate to get in touch with our knowledgeable team.