  The exploitation of clusters of galaxies as cosmological probes relies on
accurate measurements of their total gravitating mass. X-ray observations
provide a powerful means of probing the total mass distribution in galaxy
clusters, but might be affected by observational biases and rely on simplistic
assumptions originating from our limited understanding of the intracluster
medium physics. This paper is aimed at elucidating the reliability of X-ray
total mass estimates in clusters of galaxies by properly disentangling various
biases of both observational and physical origin. We use N-body/SPH simulation
of a large sample of ~100 galaxy clusters and investigate total mass biases by
comparing the mass reconstructed adopting an observational-like approach with
the true mass in the simulations. X-ray surface brightness and temperature
profiles extracted from the simulations are fitted with different models and
adopting different radial fitting ranges in order to investigate modeling and
extrapolation biases. Different theoretical definitions of gas temperature are
used to investigate the effect of spectroscopic temperatures and a power ratio
analysis of the surface brightness maps allows us to assess the dependence of
the mass bias on cluster dynamical state. Moreover, we perform a study on the
reliability of hydrostatic and hydrodynamical equilibrium mass estimates using
the full three-dimensional information in the simulation.[abridged]
