  We summarize the top-quark mass measurements from the CDF and DO experiments
at Fermilab. We combine published Run I (1992--1996) measurements with the most
precise published and preliminary Run II (2001-present) measurements using up
to 5.8 fb-1 of data, adding new analyses (the Met+Jets analysis) and updating
old ones. Taking uncertainty correlations into account, and adding in
quadrature the statistical and systematic uncertainties, the resulting
preliminary Tevatron average mass of the top quark is M_T=173.2+/-0.9 GeV/c^2.
