An unplanned release of 168,000 Ci of elemental tritium (HT) and 4700 Ci of tritium oxide (HTO) occurred on July 31, 1987 from the Savannah River Plant. The oxide fraction in the exhaust stack was determined to be 2.7%. The air concentrations of HT and HTO were also measured at 43 downwind locations. The oxide fraction varied between 2 and 3% at the plant boundary (12 miles downwind) and between 0.3% and 84% at greater downwind distances (15 to 40 miles). The increased variability of the oxide fraction with downwind distance is attributed to exchange of oxide with surface vegetation and to turbulent transfer between the surface and the boundary layer. These results are relevant to a recent study of HT oxidation based on downwind changes in the HT/HTO ratio (Bardolle, 1981).