The distribution of18O and13C isotopes in a chemical exchange system of carbon dioxide and amine carbamates has been studied. A comparison of isotope separation by 15 amines shows little dependence on the nature of the amine. Effect of amine concentration indicates that diffusion of the reacting species plays a significant role in these systems. This is in conformity with our observation that the viscosity of the amine solutions saturated with carbon dioxide increases rapidly with amine concentration.