A mechanical subcooling system operatively connectable to a transcritical R-744 refrigeration system resulting in an energy efficiency ratio of a level comparable to that of refrigeration systems using common refrigerants. Mechanical subcooling increases the refrigeration capacity without increasing the power consumption of the refrigeration system's compressors. The compressors used to provide the refrigeration capacity for the subcooling process operate at much more favorable conditions, thus having a very high energy efficiency ratio. The result is higher refrigeration capacity and lower power consumption.