Using a recent calculation of the cross sections for fine structure changing collisions during an encounter between two oxygen atoms in the ground electronic state, we determine the population of the fine structure levels of oxygen as a function of altitude for four model atmospheres representing conditions at 0¿ longitude, 45¿ latitude, at midday and midnight, and high and low solar and geomagnetic activity. We include the effect of electron impacts. The fine structure levels are shown to be in local thermodynamic equilibrium (LTE) at the local neutral atom translational temperature for altitudes up to 350 km and 400 km for midnight and midday, respectively, at low activity, and up to at least 600 km at high activity. At higher altitudes spontaneous emission causes deviation from LTE and overpopulates the lowest (J=2) level at the expense of the other two levels. ¿ American Geophysical Union 1994