  Far Ultraviolet Spectroscopic Explorer spectra of 22 Galactic halo stars are
studied to determine the amount of O VI in the Galactic halo between ~0.3 and
\~10 kpc from the Galactic mid-plane. Strong O VI 1031.93 A absorption was
detected toward 21 stars, and a reliable 3 sigma upper limit was obtained
toward HD 97991. The weaker member of the O VI doublet at 1037.62 A could be
studied toward only six stars. The observed columns are reasonably consistent
with a patchy exponential O VI distribution with a mid-plane density of
1.7x10^(-8) cm^(-3) and scale height between 2.3 and 4 kpc. We do not see clear
signs of strong high-velocity components in O VI absorption along the Galactic
sight lines, which indicates the general absence of high velocity O VI within
2-5 kpc of the Galactic mid-plane. The correlation between the H I and O VI
intermediate velocity absorption is also poor. The O VI velocity dispersions
are much larger than the value of ~18 km/s expected from thermal broadening for
gas at T~300,000 K, the temperature at which O VI is expected to reach its peak
abundance in collisional ionization equilibrium. Turbulence, inflow, and
outflow must have an effect on the shape of the O VI profiles. Kinematical
comparisons of O VI with Ar I suggest the presence of two different types of O
VI-bearing environments toward the Galactic sight lines. Comparison of O VI
with other highly-ionized species suggests that the high ions are produced
primarily by cooling hot gas in the Galactic fountain flow, and that turbulent
mixing also has a significant contribution. The role of turbulent mixing is
most important toward sight lines that sample supernova remnants like Loop I
and IV.
