Vertical enrichment profiles of stratospheric 16O16O18O and 16O18O16O (hereafter referred to as 668O3 and 686O3 respectively) have been derived from space-based solar occultation spectra recorded at 0.01 cm-1 resolution by the ATMOS (Atmospheric Trace MOlecule Spectroscopy) Fourier-transform infrared (FTIR) spectrometer. The observations, made during the Spacelab 3 and ATLAS-1, -2, and -3 shuttle missions, cover polar, mid-latitude and tropical regions between 26 to 2.6 mb inclusive (≈25 to 41 km). Average enrichments, weighted by molecular 48O3 density, of (15¿6)% were found for 668O3 and (10¿7)% for 686O3. Defining the mixing ratio of 50O3 as the sum of those for 668O3 and 686O3, an enrichment of (13¿15)% was found for 50O3 (1&sgr; standard deviation). No latitudinal or vertical gradients were found outside this standard deviation. From a series of ground-based measurements by the ATMOS instrument at Table Mountain, California (34.4 ¿N), an average total column 668O3 enrichment of (17¿4)% (1&sgr; standard deviation) was determined, with no significant seasonal variation discernable. Possible biases in the spectral intensities that affect the determination of absolute enrichments are discussed. ¿ American Geophysical Union 1996