A CO2 refrigeration system (1) includes: a compressor (3), a gas cooler (5), a temperature sensor (17) and an electronic control system (13), the electronic control system including a processor device (15) arranged to control operation of the compressor (3) according to input signals received from the temperature sensor (17), wherein the temperature sensor (17) is positioned to read an output temperature of the gas cooler. A method for controlling a compressor (3) in a CO2 refrigeration system (1) is also disclosed.