  We present a simultaneous measurement of the B0bar lifetime tau_B0 and
B0B0bar oscillation frequency Delta_md. We use a sample of about 50000
partially reconstructed B0bar --> D*+ ell- nu-bar decays identified with the
BABAR detector at the PEP-II e+e- storage ring at SLAC. The flavor of the other
B meson in the event is determined from the charge of another high-momentum
lepton. The results are tau_B0 = (1.504 +/- 0.013 (stat) {+0.018}/{-0.013}
(syst)) ps, Delta_md = (0.511 +/- 0.007 (stat) {+0.007}/{-0.006} (syst)) ps-1
