  Neutral B meson oscillations in the B0_s - anti-B0_s and B0_d - anti-B0_d
systems were studied using a sample of about 4.0 million hadronic Z decays
recorded by the DELPHI detector between 1992 and 2000. Events with a high
transverse momentum lepton were removed and a sample of 770 k events with an
inclusively reconstructed vertex was selected. The mass difference between the
two physical states in the B0_d - anti-B0_d system was measured to be:
  \Delta m_d = (0.531 +/- 0.025 (stat.) +/- 0.007 (syst.)) ps^{-1}.
  The following limit on the width difference of these states was also
obtained:
  |\Delta\Gamma_{B_d}| / \Gamma_{B_d} < 0.18 at 95% CL.
  As no evidence for B0_s - anti-B0_s oscillations was found, a limit on the
mass difference of the two physical states was given:
  \Delta m_s > 5.0 ps^{-1} at 95% CL.
  The corresponding sensitivity of this analysis is equal to 6.6 ps^{-1}.
