  We study the uncertainties in the MSbar bottom quark mass determination using
relativistic sum rules to O(alpha_S^2). We include charm mass effects and
secondary b bbar production and treat the experimental continuum region more
conservatively than previous analyses. The PDG treatment of the region between
the resonances Upsilon (4S) and Upsilon (5S) is reconsidered. Our final result
reads: m_b(m_b)=(4.20 \pm 0.09) GeV.
