  We present an all-sky catalog of diffuse O VII and O VIII line intensities,
extracted from archival XMM observations. The O VII and O VIII intensities are
typically ~2-11 and <~3 ph/cm^2/s/sr (LU), respectively, although much brighter
intensities were also recorded. Our data set includes 217 directions observed
multiple times by XMM. The time variation of the intensities from such
directions may be used to constrain SWCX models. The O VII and O VIII
intensities typically vary by <~5 and <~2 LU between repeat observations,
although several intensity enhancements of >10 LU were observed. We compared
our measurements with SWCX models. The heliospheric SWCX intensity is expected
to vary with ecliptic latitude and solar cycle. We found that the observed
oxygen intensities generally decrease from solar maximum to solar minimum, both
at high ecliptic latitudes (as expected) and at low ecliptic latitudes (not as
expected). The geocoronal SWCX intensity is expected to depend on the solar
wind proton flux and on the sightline's path through the magnetosheath. The
intensity variations seen in directions that have been observed multiple times
are in poor agreement with the predictions of a geocoronal SWCX model. The
oxygen lines account for ~40-50% of the 3/4 keV X-ray background that is not
due to unresolved AGN, in good agreement with a previous measurement. However,
this fraction is not easily explained by a combination of SWCX emission and
emission from hot plasma in the halo. The line intensities tend to increase
with longitude toward the inner Galaxy, possibly due to an increase in the
supernova rate in that direction or the presence of a halo of accreted material
centered on the Galactic Center. The variation of intensity with Galactic
latitude differs in different octants of the sky, and cannot be explained by a
single simple plane-parallel or constant-intensity halo model. (Abridged)
