  We have conducted a survey of FUSE spectra of 235 Galactic B-type stars in
order to determine the boundaries in the H-R diagram for the production of the
superion O VI in their winds. By comparing the locations and morphology of
otherwise unidentified absorption features in the vicinity of the O VI
resonance doublet with the bona fide wind profiles seen in archival IUE spectra
of the resonance lines of N V, Si IV and C IV, we were able to detect
blueshifted O VI lines in the spectra of giant and supergiant stars with
temperature classes as late as B1. No features attributable to O VI were
detected in dwarfs later than B0, or in stars of any luminosity class later
than B1, although our ability to recognize weak absorption features in these
stars is severely restricted by blending with photospheric and interstellar
features. We discuss evidence that the ratio of the ion fractions of O VI and N
V is substantially different in the winds of early B-type stars than O-type
stars.
