The average lifetime of B hadrons was measured using data collected with the DELPHI detector at the LEP collider during 1991 and 1992. The measurement was performed using two different analyses. The first method was an improvement on a previous technique, which used charged particle impact parameter distributions. This analysis measured an average lifetime for B hadrons of tau(B) = 1.542 +/- 0.021 (stat.) +/- 0.045 (syst.) ps. (1) The second method was based on a new technique, which used inclusively reconstructed secondary vertices to measure tau(B) = 1.599 +/- 0.014 (stat.) +/- 0.035 (syst.) ps. (2) Taking into account both the statistical and systematic correlations, the results of these two methods were combined to give an average lifetime for B hadrons of tau(B) = 1.582 +/- 0.012 (stat.) +/- 0.032 (syst.) ps. (3)
