Mon - Fri | 7AM - 5PM CST

Understanding Base Oils, 1 of 2

The very important, majority component of any lubricant - the Base Oil

Lubrication is a vital aspect of the proper functioning and longevity of machinery, whether in the automotive, industrial, or other sectors. At the heart of every lubricant is a base oil, which makes up to 80% of any engine lubricant and 90% of any industrial lubricant. A base oil provides the fundamental lubricating properties needed to reduce friction, wear, and heat between moving parts. Base oils can be derived from various sources, including mineral, synthetic, vegetable, and biodegradable oils. They also possess a range of physical and chemical properties that must be considered when selecting the appropriate base oil for a particular application. In this article, we will explore the different types of base oils and their properties. In the future part two of this segment, we will cover proper base oil applications and the factors that should be considered when choosing the right base oil for optimal lubrication.

Base Oil Types

There are several types of base oils available in the market, each with its own set of characteristics and properties. The main types of base oils include:

Mineral Base Oils:

Mineral base oils are derived from crude oil through a refining process. They are widely used in lubricants due to their excellent lubrication properties, high availability, and low cost. Mineral base oils are suitable for many applications.

Synthetic Base Oils:

Synthetic base oils are chemically synthesized to achieve specific properties such as high-temperature stability, low volatility, and excellent oxidation resistance. These base oils can be customized to meet specific requirements and are often used in high-performance applications such as aerospace, racing, and extreme temperature conditions.

Vegetable Base Oils:

Vegetable base oils are derived from various plant sources, such as rapeseed, sunflower, and soybean oil. These oils are environmentally friendly, biodegradable, and non-toxic, making them a popular choice for applications where environmental concerns are important, such as in the food industry and maritime industries and as biodegradable lubricants.

Biodegradable Base Oils:

Biodegradable base oils are designed to break down naturally and do not harm the environment. These base oils can be derived from mineral, synthetic, or vegetable sources, and are suitable for applications where environmental considerations are a high priority, such as in marine and forestry applications.

Each type of base oil has its own advantages and disadvantages, and the selection of the appropriate base oil for a particular application depends on several factors such as the operating conditions, equipment type, and environmental considerations. There was significant variability in the quality and performance of base oils. This made it difficult for lubricant blenders and end users to know exactly what they were getting and how it would perform in different applications. The industry needed a way of categorizing the different base oils. We will look at one of the most used base oil classification systems.

The American Petroleum Institute (API) has developed a classification system for base oils, known as the API Base Oil Classification System. This system categorizes base oils into five groups, based on their properties and characteristics, with each group representing a different level of performance and quality. Understanding the advantages and disadvantages of each API base oil group can help in selecting the most appropriate base oil for a specific application. The following table provides a summary of the advantages and disadvantages of each API base oil group, including their availability, cost, lubricity, and performance at high and low temperatures. It is important to note that the selection of a base oil should be based on the specific requirements of the application, including equipment compatibility, operating conditions, and environmental considerations.

API Base Oil Classes

* Group I base oils used in the USA and Europe have declined significantly due to the availability of Group II and Group III base oils and increased environmental requirements. Group I base oils are still used in Russia, areas of Asia, and many Middle Eastern countries.

Properties of Base Oils

The properties of a base oil play a critical role in determining its suitability for a particular application. Some of the key properties of base oils include:


Viscosity refers to the oil's resistance to flow and is considered the most important physical property of a lubricant. Viscosity is typically measured at two temperatures, 40°C and 100°C, and two of the most widely used classification systems are ISO (International Standards) and SAE (Society of Automotive Engineers). The results are typically reported as cSt (centistokes). The correct viscosity grade must be selected to ensure that the oil flows freely and provides adequate lubrication.

Oxidation stability:

Oxidation stability refers to the ability of the oil to resist breakdown due to exposure to air and high temperatures. An oil with good oxidation stability will resist the formation of harmful sludge and varnish deposits, which can lead to engine or equipment failure. The importance of oxidative stability in turbine oils cannot be overstated, as the oil is continuously exposed to extreme temperatures, pressures, and oxygen-rich environments. When exposed to these conditions, the oil can begin to oxidize, leading to the formation of harmful deposits, sludge, and varnish. This degradation can cause increased wear and tear on turbine components, reduced system efficiency, and increased maintenance costs. To ensure maximum equipment protection, performance, and lifespan, turbine oils must have exceptional oxidative stability to resist oxidation and maintain their performance over extended periods. Therefore, it is crucial to choose a turbine oil with high oxidative stability and implement regular oil analysis and proper fluid maintenance practices to ensure optimal turbine performance, avoid costly maintenance and downtime, and extend the service life of the oil.


Volatility refers to the oil's tendency to evaporate at high temperatures. Base oils with high volatility can lead to oil consumption and contribute to air pollution. High-performance applications require base oils with low volatility to ensure the oil remains in the system and continues to provide adequate lubrication.

Pour point:

Pour point refers to the temperature at which the oil becomes too viscous to flow. A low pour point is essential for oils used in cold environments, as it ensures the oil remains fluid and can flow through the system.

Additive solubility:

Additive solubility refers to the ability of the oil to dissolve additives such as detergents, dispersants, and anti-wear agents. A base oil with good additive solubility will ensure that the additives remain suspended in the oil, providing maximum protection to the system.

The properties of a base oil can be improved through the addition of specialized additives, which can enhance its performance and extend its useful life. However, it is essential to select a base oil that possesses the necessary properties for a particular application to ensure optimal lubrication and equipment protection. The combination of the correct group of base oil and its properties determine its useful application, which we will discuss in Part II of this segment!

Thu May 25 2023, by Gene Wagenseller
Go Back