Various field-test systems using carbon dioxide as the only refrigerant have been installed since December 2001. In this paper we will analyse an 'all-CO2' supermarket, which has been operating in the North of Italy since January 2003. The seasonal COP is calculated, based on prior laboratory measurements, and a comparison is made with a conventional direct expansion system using R404A. The total annual energy consumption of the installed CO2 system is estimated to be about 10% higher than the direct expansion R404A solution. It is still possible to further improve efficiency and approach the efficiency of present R404A systems. These improvements are identified. The cost of the CO2 installation is compared to the cost of an equivalent direct expansion R404A installation, the most economic among the various present types of commercial refrigeration systems. Because of the lack of suitable mass-produced components, the CO2 installation is estimated to be, today, about 20% more expensive.