  We compare X-ray and caustic mass profiles for a sample of 16 massive galaxy
clusters. We assume hydrostatic equilibrium in interpreting the X-ray data, and
use large samples of cluster members with redshifts as a basis for applying the
caustic technique. The hydrostatic and caustic masses agree to better than
$\approx20\%$ on average across the radial range covered by both techniques
$(\sim[0.2-1.25]R_{500})$. The mass profiles were measured independently and do
not assume a common functional form. Previous studies suggest that, at
$R_{500}$, the hydrostatic and caustic masses are biased low and high
respectively. We find that the ratio of hydrostatic to caustic mass at
$R_{500}$ is $1.20^{+0.13}_{-0.11}$; thus it is larger than 0.9 at
$\approx3\sigma$ and the combination of under- and over-estimation of the mass
by these two techniques is $\approx10\%$ at most. There is no indication of any
dependence of the mass ratio on the X-ray morphology of the clusters,
indicating that the hydrostatic masses are not strongly systematically affected
by the dynamical state of the clusters. Overall, our results favour a small
value of the so-called hydrostatic bias due to non-thermal pressure sources.
