Interest in the supercritical carbon dioxide (S-CO2) Brayton cycle technology is gradually increasing due to high efficiency at moderate turbine inlet temperature and potential to achieve high compactness of the whole power conversion system. As a part of research activities on the S-CO2 Brayton cycle technology development, Supercritical CO2 Pressurization Experiment (SCO2PE) facility was constructed for lab scale CO2 compression experiment near the critical point. SCO2PE facility operation is focused on resolving issues in a compressor design and operation near the critical point of CO2. From the SCO2PE operation experience, performance measurement uncertainty issues in a low pressure ratio compressor were identified and these issues become generic if a compressor operates near the critical point. Very high uncertainty on performance measurement was observed due to the peak region in thermodynamic property variation of CO2 near the critical point and low pressure ratio operation of the compressor. High pressure ratio compressor design and operation can mitigate high uncertainty issues in performance measurement. However, low pressure ratio operation cannot be ignored since low pressure ratio operation is always involved during a part load operation or transient operation of a power conversion system. Thus, an alternative approach was suggested to secure reliability of performance estimation from the basic measurement.