A measurement of B meson lifetimes is presented using data collected from 1991 to 1993 by the DELPHI detector at the LEP collider, Samples of events with a D meson and a lepton in the same jet are selected where ($) over bar D(0)l(+) and D*(-)l(+) events originate mainly from the semileptonic decays of B+ and B-0 mesons, respectively. From the reconstructed B decay length and the estimated B momentum, taking into account the dilution due to B decays into ($) over bar D**l(+)v, the following B meson lifetimes and lifetime ratio are measured: tau(B+) = 1.61(-0.16)(+0.16) (stat.) +/- 0.12 (syst.) ps tau(B-0) = 1.61(-0.13)(+0.14) (stat.) +/- 0.08 (syst.) ps tau (B+)/tau(B-0) = 1.00(-0.15)(+0.17) (stat.) +/- 0.10 (syst.) and an average lifetime of B+ and B-0 mesons is obtained: tau(B) = 1.61(-0.07)(+0.08) (stat.) +/- 0.05 (syst.) ps
