The theoretical performances of HCFC123, HFC134a, CFC11, and CFC12 have been assessed as coolants. For a specific amount of desired energy, more compression work is required for HCFC123 and HFC134a than for CFC11 and CFC12. The differences are not very significant at high evaporation temperatures and hence HCFC123 and HFC134a should not be excluded as alternative coolants. There is an optimum evaporation temperature for each condensation temperature which yields the highest exergetic efficiency.