  We present an investigation of the effects of asphericity on the estimates of
total mass and gas mass fraction in galaxy clusters from X-ray observations. We
model the aspherical shape of galaxy clusters by a triaxial model and compare
the true total mass and the true total gas mass fraction with the corresponding
quantities obtained with the assumption of spherical symmetry. In the triaxial
model we allow the extent along the line of sight to vary in order to describe
elongated and compressed cluster shapes. Using a sample of 10 ROSAT clusters
and a recent CHANDRA observation we find the following results. For prolate or
oblate shapes the difference between triaxial and spherical model both in the
mass and in the gas mass fraction are negligible (less than 3 %). For more
aspherical shapes the total mass is underestimated (overestimated) in the
centre, if the cluster is compressed (elongated). The gas mass fraction is
overestimated for compressed clusters and slightly underestimated for elongated
clusters. Comparing X-ray masses with gravitational lensing estimates, we find
that elongations along the line of sight can resolve discrepancies of masses
determined by the two different methods of up to ~30 %. The combination of
Sunyaev-Zel'dovich and X-ray observations is useful to measure the elongation
of the cluster along the line of sight. As an application, we estimate the
elongation of the cluster CL0016+16 with two different approaches,
Sunyaev-Zel'dovich measurements and comparison of weak lensing and X-ray
masses, and find reasonable agreement.
