This article focuses on lubricants classified as either internal combustion engine or nonengine lubricants, and the lubricant additives. The functional groups of chemically active and inert additives, as well as friction modifiers and other additives, are described in detail. The chemically active additives include dispersants, detergents, antiwear, and extreme-pressure agents, oxidation inhibitors, and rust and corrosion inhibitors. The chemically inert additives include emulsifiers, demulsifiers, pour-point depressants, foam inhibitors, and viscosity improvers. The article also discusses the multifunctional nature of additives and concludes with information on lubricant formulation.

The function of lubricants is to control friction and wear in a lubricating system containing machine elements such as gears and bearings. This article discusses the basic properties of lubricants to help scientists and engineers understand the principles behind lubricant selection. It reviews the functions of additives, such as friction modifiers, antiwear additives, viscosity modifiers, corrosion inhibitors, oxidation inhibitors, dispersants, and detergents. The article discusses the physical properties of liquid lubricants and the performance characteristics of lubricants. It describes the most common lubricant categories and provides information on the health and safety aspects of using liquid lubricants. The article concludes with a discussion on the lubricant-application method that plays a vital role in how the lubricant functions.