Since base oil is considered the main component of a lubricant, paying attention to its structure, in addition to identifying its application, plays a significant role in the quality of the lubricant. 

In fact, lubricants such as engine oils are made of base oil and those additives which are added to improve the base oil characteristics.
Therefore, it is essential, above all, to pay meticulous attention to the characteristics of base oil for producing the required components of a lubricant.

API is the most common base oil classification. According to this Classification, base oils are categorized based on their origin, refining and production processes, viscosity index, sulfur content and the saturation percentage.