  We present the reconstruction of hydrostatic mass profiles in 13 X-ray
luminous galaxy clusters that have been mapped in their X-ray and SZ signal out
to $R_{200}$ for the XMM-Newton Cluster Outskirts Project (X-COP). Using
profiles of the gas temperature, density and pressure that have been spatially
resolved out to (median value) 0.9 $R_{500}$, 1.8 $R_{500}$, and 2.3 $R_{500}$,
respectively, we are able to recover the hydrostatic gravitating mass profile
with several methods and using different mass models. The hydrostatic masses
are recovered with a relative (statistical) median error of 3% at $R_{500}$ and
6% at $R_{200}$. By using several different methods to solve the equation of
the hydrostatic equilibrium, we evaluate some of the systematic uncertainties
to be of the order of 5% at both $R_{500}$ and $R_{200}$. A Navarro-Frenk-White
profile provides the best-fit in nine cases out of 13, with the remaining four
cases that do not show a statistically significant tension with it. The
distribution of the mass concentration follows the correlations with the total
mass predicted from numerical simulations with a scatter of 0.18 dex, with an
intrinsic scatter on the hydrostatic masses of 0.15 dex. We compare them with
the estimates of the total gravitational mass obtained through X-ray scaling
relations applied to $Y_X$, gas fraction and $Y_{SZ}$, and from weak lensing
and galaxy dynamics techniques, and measure a substantial agreement with the
results from scaling laws, from WL at both $R_{500}$ and $R_{200}$ (with
differences below 15%), from cluster velocity dispersions, but a significant
tension with the caustic masses that tend to underestimate the hydrostatic
masses by 40% at $R_{200}$. We also compare these measurements with predictions
from alternative models to the Cold Dark Matter, like the "Emergent Gravity"
and MOND scenarios.
