Lubricants are used to reduce friction, partially or completely prevent wear and prevent temperature rise. In terms of friction, the function of the lubricant is different for various friction states. Since the oil layer between the surfaces in fluid friction completely separates the surfaces from each other, the important issue here is the viscosity of the oil. For this reason, in the case of fluid friction, generally liquid and sometimes gaseous lubricants are used. In the case of boundary friction, the adhesion ability of the lubricant and, accordingly, its chemical composition is important. For this reason, solid and liquid lubricants with additives are used in case of boundary friction. An important function of lubricants, especially liquid oils, is to transfer the heat generated on the surfaces due to friction to the outside with the flow of the oil. Lubricants can be divided into four groups according to their physical states: solid, liquid, semi-solid and gaseous lubricants.