A1 / B1 - Energy saving, long life oil - "New Japanese and American cars";
A3 / B3 - Motor oils (European cars and older Japanese and American cars) outside diesel engines with direct fuel injection;
A3 / B4 - engine oils including diesel fuel injection with direct fuel injection;
A5 / B5 - energy efficient, long life oils for high performance engines;

C1 - Oil for engines requiring low SAPS and lower viscosity index High Temperature Tar (HTHS);
C2 - Oil engines requiring medium load and low viscosity index high temperature tars (HTHS);
C3 - Oils for engines requiring medium to high viscosity index high temperature tars (HTHS);
C4 - Oils for engines that require low SOAPS and higher viscosity index high temperature tars (HTHS);
E4, E6, E7 i E9 - Classification depends primarily on vehicle emission standards and oil change intervals.

The advantage of ACEA standards is the highly elaborate and restrictive criteria for assigning oils to groups (closer and more accurate than API and ILSAC) and the absence of very complex compatibility rules.

Simplifying:

A3 / B3 oil can be replaced with A3 / B4;
The requirements of A1 / B1 and A5 / B5 standards are the same in addition to one parameter (HTHS, which has a wider range of A1 / B1 than A5 / B5), so most OILS meet both standards (only some low viscosity A1 / B1 oils do not meet A5 / B5 standards);