CO2 refrigeration systems, as used e.g. for supermarket applications, often encounter a drastical decrease of COP when operation moves into a transcritical mode. There are several options to enhance the system efficiency to reduce this penalty. All of them influence the optimum value for discharge and intermediate pressure. This paper discusses these influences for parallel compression and for an additional booster compressor. For comparison a system simulation was performed. The compressor model in the simulation is based on a data map of a currently available compressor. As a result the system’s efficiency improvement potential of both methods is presented under consideration of optimized operation conditions.