The term lubricant refers to solid, liquid, and gaseous substances whose application affects the reduction of friction between contact surfaces in relative motion, and in the case of marine diesel engines, they are used to lubricate almost all moving mechanical elements. Since marine diesel engines are complex machines that generate a large amount of heat during operation, the use of high-quality lubricants is required. Such lubricants enable heat dissipation (to maintain normaln operating temperature), reduce friction and wear, and favor the creation of a thin oil film that protects engine parts. Lubricating oils consist of base oils and certain additives. Depending on the type of oil, different additives are used, and the most important are viscosity index improvers, pour point inprovers, anti-foaming agents, additives for protection against corrosion, oxidation, extreme pressures, and other additives. To extend the service life of diesel engines, along with proper lubrication and selection of the appropriate type of lubricant, it is important to regulary carry out an oil analysis, which is carried out during routine maintenance to obtain significant and accurate information about the condition of the lubricant and the machine.