  Using the Goddard High Resolution Spectrograph (GHRS) onboard HST, we have
obtained high S/N echelle observations of the weak interstellar O I 1356 A
absorption toward the stars Gamma Cas, Epsilon Per, Delta Ori, Epsilon Ori, 15
Mon, Tau CMa, and Gamma Ara. In combination with previous GHRS measurements in
six other sightlines (Zeta Per, Xi Per, Lambda Ori, Iota Ori, Kappa Ori, and
Zeta Oph), these new observations yield a mean interstellar gas-phase oxygen
abundance (per 10$^6$ H atoms) of 10$^6$ O/H = 319 +/- 14. The largest
deviation from the mean is less than 18%, and there are no statistically
significant variations in the measured O abundances from sightline to sightline
and no evidence of density-dependent oxygen depletion from the gas phase.
Assuming various mixtures of silicates and oxides, the abundance of
interstellar oxygen tied up in dust grains is unlikely to surpass 10$^6$ O/H
$\approx$ 180. Consequently, the GHRS observations imply that the total
abundance of interstellar oxygen (gas plus grains) is homogeneous in the
vicinity of the Sun and about 2/3 of the solar value of 10$^6$ O/H = 741 +/-
130. This oxygen deficit is consistent with that observed in nearby B stars and
similar to that recently found for interstellar krypton with GHRS. Possible
explanations for this deficit include: (1) early solar system enrichment by a
local supernova, (2) a recent infall of metal-poor gas in the local Milky Way,
or (3) an outward diffusion of the Sun from a smaller galactocentric distance.
