  We consider single-top-quark production via the weak process $q\bar q to
t\bar b$ at hadron colliders. This process may provide the best measurement of
the magnitude of the Cabbibo-Kobayashi-Maskawa matrix element $V_{tb}$. We show
that a signal can potentially be observed at the Fermilab Tevatron with 3
$fb^{-1}$ of integrated luminosity. In contrast, the signal is masked at the
CERN Large Hadron Collider by top-quark pair production and single-top-quark
production via $W$-gluon fusion.
