The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993, B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic Z(0) decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1 +/- 0.3%, and 83% (70%) of the events measured as neutral (charged) came from neutral (charged) B's, The mean lifetimes of charged and neutral B hadrons were found to be 1.72 +/- 0.08 (stat.) +/- 0.06 (syst.) ps and 1.58 +/- 0.11 (stat.) +/- 0.09 (syst.) ps respectively. The ratio of their lifetimes, tau((charged))/tau((neutral)), was 1.09(-0.10)(+0.11) (stat.)+/-0.08 (syst.). By making assumptions about the B-s(0) and Lambda(b)(0) states, the B+ and B-0 meson life-times were determined to be tau(B)+ = 1.72 +/- 0.08 (stat.) +/- 0.06 (syst.) ps and tau(B)0 = 1.63 +/- 0.14 (stat.) +/- 0.13 (syst.) ps and the ratio of their lifetimes was: tau(B)+/tau(B)0 = 1.06(-0.11)(+0.13) +/- 0.10. The mean B lifetime was also deduced to be <tau(B)> = 1.64 +/- 0.06 (stat.) +/- 0.04 (syst.) ps.
