  We make an analysis of the hadronic invariant mass spectrum in inclusive
charmless semileptonic B meson decays in a QCD-based approach. The decay width
is studied as a function of the invariant mass cut. We examine their
sensitivities to the parameters of the theory. The theoretical uncertainties in
the determination of $|V_{ub}|$ from the hadronic invariant mass spectrum are
investigated. A strategy for improving the theoretical accuracy in the value of
$|V_{ub}|$ is described.
