  We present the results of the analysis of the internal velocity dispersions,
\sigma_v, for the CNOC sample of distant galaxy clusters, based on an
interlopers removal algorithm, which is different from that originally applied
by Carlberg et al. (1996, C96). We find that the resulting \sigma_v values are
consistent within <10% with the original C96 estimates. This result points in
favor of a substantial robustness of currently applied methods for optical
studies of the internal cluster dynamics. The resulting distribution of
velocity dispersions is used to trace the redshift evolution of the cluster
abundance with the aim of constraining the matter density parameter, \Omega_m.
We find that constraints on \Omega_m are very sensitive to the adopted value of
\sigma_8, as obtainable from the local cluster abundance: as \sigma_8 varies
from 0.5 to 0.6 (for Omega_m=1), the best fitting Omega_m varies in the range
0.3-1.0.
