Qualified Lubricant products must be certified by several major international organizations or institutions, especially the North American API (American Petroleum Institute) and the European ACEA (European Automobile Manufacturers Association). The most common standard is API standard.
According to the standard used for lubricating oil engine passenger cars, the grade number of lubricating oil begins with the capital letter S, followed by a capital letter indicating lubricant performance grade. For example, the earliest classification criteria are "SA", then "SB", then "SC", and so on. Currently, the current standard is "SL". For the four-stroke diesel engine, there are corresponding API standards, labeling methods similar to the petrol engine oil standard, only the first letter S in the C can be replaced. The current four-stroke diesel Engine API standard is "CI-4". The certification process for these standards is rigorous and must be achieved through a large number of engine and laboratory experiments designated by these organizations and engine manufacturers.