Lubricants are essential substances in modern industries, automobiles, and machinery because they reduce friction and wear between moving surfaces, protect against corrosion, dissipate heat, and improve the efficiency and lifespan of mechanical systems. In environmental chemistry, the study of lubricants is not only concerned with their chemical structure and working mechanism but also with their ecological implications, biodegradability, and potential environmental hazards. Understanding their mechanism, classification, and properties provides insight into how these substances function and how they are designed for specific applications. The mechanism of lubricants primarily revolves around reducing friction and wear. When two surfaces move against each other, direct metal-to-metal contact can cause excessive wear, heat generation, and energy loss. Lubricants form a thin film or layer between these surfaces, preventing direct contact and thereby minimizing friction. The lubrication mechanism can be explained through several theories. The first is fluid-film lubrication, where a continuous film of lubricant completely separates the two surfaces. In this regime, the load is carried by the pressure generated in the fluid film, which is typically seen in hydrodynamic lubrication such as in journal bearings. The second is boundary lubrication, which occurs when a thin layer of lubricant molecules, often enhanced with additives, remains adsorbed on the surfaces even when the fluid film is not sufficient to separate them completely. This situation arises in high-load or low-speed conditions. The third is mixed lubrication, which is an intermediate state where partial fluid-film lubrication coexists with some surface asperity contact, often seen in practical machines during start-up or varying load conditions. Besides these, elastohydrodynamic lubrication is another mechanism, where elastic deformation of surfaces and high-pressure lubricant films come into play, particularly in rolling contacts like gears and roller bearings. Thus, the mechanism of lubrication is dynamic and depends on operating conditions such as load, speed, and temperature. The classification of lubricants can be done based on their state, source, or application. The broadest division is into liquid, semi-solid, and solid lubricants. Liquid lubricants, commonly oils, are the most widely used and can be further classified as mineral oils, synthetic oils, and biodegradable oils. Mineral oils are derived from the refining of petroleum and are the most common type, being economical and versatile. Synthetic oils are chemically engineered lubricants, such as polyalphaolefins, esters, and silicones, offering superior thermal stability, oxidation resistance, and performance in extreme conditions. Biodegradable oils are plant-based or specially synthesized to minimize environmental harm, often used in eco-sensitive applications. Semi-solid lubricants,