What the ACEA sequences are
The ACEA oil sequences are a set of European performance classes for engine oils, published by the European Automobile Manufacturers’ Association. Rather than a single standard, they form a family of categories grouped by engine type and aftertreatment needs. Each class defines a level of performance that an oil must be tested against, which is why European vehicle makers frequently reference ACEA classes in their requirements.
The categories are organised into broad letter groups. The A/B group covers oils for gasoline and diesel passenger-car engines. The C group covers low-SAPS oils — meaning reduced sulphated ash, phosphorus, and sulphur — which are designed to be friendlier to catalytic converters and diesel particulate filters. The E group covers heavy-duty diesel applications such as commercial vehicles.
How the classes differ
Because each group targets different demands, the classes are not freely interchangeable. A C-class low-SAPS oil is formulated with aftertreatment protection in mind and is not the same as an A/B oil, even if the viscosity grade matches. Choosing the wrong class can be unsuitable for engines with sensitive emissions hardware.
It is best to think of the ACEA class and the viscosity grade as two separate pieces of information. The grade — for example 5W-30 — describes flow behavior, while the ACEA class describes the performance and chemistry level. An oil should meet the class your manual calls for AND the correct grade.
What to follow
ACEA sequences are revised over time, and individual classes within each group carry numeric identifiers that change between revisions. For that reason this overview keeps to the general structure rather than specific sub-numbers.
For the exact class your vehicle needs, rely on the owner’s manual. It is the authoritative source and accounts for the specific engine and emissions setup your car uses.