The kinetic and equilibrium fractionation effects for 13 C during CO 2 gas transfer (ε k and ε ag−g ) have been measured in acidified distilled water. The equilibrium fractionation effects between bicarbonate and carbonate and gaseous C0 2 (εHCO 3 −g and εCO 3−g ) have been measured in NaHC0 3 and NaHC0 3 + Na 2 C0 3 solutions, respectively, from 5° to 25°C. The measured fractionations, except εCO 3 −g , agreed with earlier work to within 0.2‰. εCO 3 −g was about 2‰ smaller than most values previously reported. The temperature dependence of the fractionation for 13 C between bicarbonate and carbonate and gaseous CO 2 was found to be εHCO 3 −g = −(0.141 ± 0.003)T(°C) + 0.05)‰ and εCO 3 −g = −(0.052 ± 0.03) T(°C)E+ (7.22 ± 0.46)‰ respectively. The fractionation during gas dissolution was εCO 3 −g = −0.03)T(°C) + (1.31 ± 0.06%. and the kinetic effect during gas transfer, ε k , was −0.81 ± 0.16‰ at 21°C and −0.95 ± 0.20‰ at 5°C.The equilibrium fractionation between total DIC in seawater and CO 2 in air (ε DIC−g ) was measured and compared with that calculated from the concentration of aqueous CO 2 , HC0 3 − and CO 3 = and individual fractionations between the three C species and CO 2 gas. The measured and calculated results showed a significant difference of up to 0.2‰. We hypothesize that carbonate ion complexes likely complicate the calculation of ε DIC−g from individual C species. We obtain the following empirical function of ε DIC−g in seawater vs. temperature and the carbonate fraction (fCO 3 ), ε DIC−g = (0.014 ± 0.01) Tf CO 3 − (0.105 ± 0.002) T + (10.53 ± 0.05)%., when 0.05 < fCO 3 < 0.20and5°C< T < 25°C