  The X-ray emission of O-type stars was first discovered in the early days of
the Einstein satellite. Since then many different surveys have confirmed that
the ratio of X-ray to bolometric luminosity in O-type stars is roughly
constant, but there is a paucity of studies that account for detailed
information on spectral and wind properties of O-stars. Recently a significant
sample of O stars within our Galaxy was spectroscopically identified and
presented in the Galactic O-Star Spectroscopic Survey (GOSS). At the same time,
a large high-fidelity catalog of X-ray sources detected by the XMM-Newton X-ray
telescope was released. Here we present the X-ray catalog of O stars with known
spectral types and investigate the dependence of their X-ray properties on
spectral type as well as stellar and wind parameters. We find that, among the
GOSS sample, 127 O-stars have a unique XMM-Newton source counterpart and a Gaia
data release 2 (DR2) association. Terminal velocities are known for a subsample
of 35 of these stars. We confirm that the X-ray luminosities of dwarf and giant
O stars correlate with their bolometric luminosity. For the subsample of O
stars with measure terminal velocities we find that the X-ray luminosities of
dwarf and giant O stars also correlate with wind parameters. However, we find
that these correlations break down for supergiant stars. Moreover, we show that
supergiant stars are systematically harder in X-rays compared to giant and
dwarf O-type stars. We find that the X-ray luminosity depends on spectral type,
but seems to be independent of whether the stars are single or in a binary
system. Finally, we show that the distribution of log(Lx/Lbol) in our sample
stars is non-Gaussian, with the peak of the distribution at log(Lx/Lbol) around
-6.6.
