  We report on measurements of the ttbar production cross section at a
center-of-mass energy of 1.96 TeV at the D0 experiment during Run II of the
Fermilab Tevatron collider. We use candidate events in lepton+jets and dilepton
final states. In the most sensitive channel (lepton+jets channel), a neural
network algorithm that uses lifetime information to identify b-quark jets is
used to distinguish signal from background processes. We also present
measurements of single top quark production at D0 using several multivariate
techniques to separate signal from background.
