Trichlorofluoromethane (CCl3F; CFC-11) and dichlorodifluoromethane (CCl2F2; CFC-12) have been widely used as tracers of oceanic circulation and mixing on decadal timescales. In order to estimate their transfer rate across the air-sea interface, liquid-phase diffusion coefficients are needed. In this study the diffusivities of CFC-11 and CFC-12 in pure water were measured over the temperature range 0.6--30 ¿C. Diffusivities of CFC-11 in pure water ranged from (5.24¿0.25)¿10-6 cm2 s-1 at 0.6 ¿C to (1.13¿0.05)¿10-5 cm2 s-1 at 30.3 ¿C and a fit to the data yielded the equation DCFC-11=0.015 exp(-18.1/RT), where R is the universal gas constant in kJ mol-1 K-1 and T is the temperature in Kelvin. Diffusivities of CFC-12 in pure water ranged from (5.38¿0.22)¿10-6 cm2 s-1 at 0.6 ¿C to (1.26¿0.05)¿10-5 cm2 s-1 at 30.3 ¿C and the temperature dependence can be expressed as DCFC-12=0.036 exp(-20.1/RT). The estimated uncertainty in both equations is <3%. Experiments were also carried out in seawater for each compound. For CFC-11 the diffusivity in seawater was not significantly different from that in pure water. However, the diffusivity of CFC-12 in seawater was found to be 7.2¿3.0% lower than that in pure water. Schmidt numbers for both CFC-11 and CFC-12 in pure water and seawater were estimated from the data. ¿ 1998 American Geophysical Union