Combination of CDF and DO results on the mass of the top quark using up to 5.8~fb-1 of data

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.