  A measurement of the t t-bar production cross section in pp collisions at
sqrt(s) = 7 TeV is presented. The results are based on data corresponding to an
integrated luminosity of 2.3 inverse femtobarns collected by the CMS detector
at the LHC. Selected events are required to have one isolated, high transverse
momentum electron or muon, large missing transverse energy, and hadronic jets,
at least one of which must be consistent with having originated from a b quark.
The measured cross section is 158.1 +/- 2.1 (stat.) +/- 10.2 (syst.) +/- 3.5
(lum.) pb, in agreement with standard model predictions.
