During the Geosecs expedition in the Atlantic and the Pacific oceans, more than 100 stations were occupied for the measurement of surface radon profiles. The radon deficiency in these profiles gives estimates of the gas transfer rate across the sea-air interface. The global mean transfer rate is estimated to be 2.9 m/d (at 20¿ C) which is corresponding to a hypothetical stagnant films thickness of about 36 microns. No clear relationship can be found between the gas exchange rate and wind speed. The CO2 exchange rate as determined by the radon method is 80% of that given by the distributions of natural and of bomb-produced radiocarbon. One possible explanation may be that the Geosecs radon measurements were made during periods of lower than average wind speed. Another is that the conversion of CO2 to HCO3- is catalyzed within the sea.