O2/N2 is measured in the Cape Grim Air Archive (CGAA), a suite of tanks filled with background air at Cape Grim, Tasmania (40.7 ¿S, 144.8 ¿E) between April 1978 and January 1997. Derived trends are compared with published O2/N2 records and assessed against limits on interannual variability of net terrestrial exchanges imposed by trends of Δ 13C in CO2. Two old samples from 1978 and 1987 and eight from 1996/97 survive critical selection criteria and give a mean 19-year trend in Δ(O2/N2) of -16.7¿0.5 per meg yr-1, implying net storage of +2.3¿0.7 GtC (1015 g carbon) yr-1 of fossil fuel CO2 in the oceans and +0.2¿0.9 GtC yr-1 in the terrestrial biosphere. The uptake terms are consistent for both O2/N2 and Δ13C tracers if the mean 13C isotopic disequilibrium flux, combining terrestrial and oceanic contributions, is 93¿15 GtC ? yr-1. ¿ 1999 American Geophysical Union