A new method for graphical determination of mass transfer (saturation) time in a deep bubble bed (BB) was developed. It is based on the spatial distribution of the local liquid-phase concentrations C-1.(t) measured by means of an electrical conductivity probe. The raw C-1.(t) data were obtained in a 0.289-m-ID bubble column equipped with a perforated plate gas distributor (31 holes x o2 x 10(-1) m). Three different clear liquid heights (L-0 = 0.56, 1.12 and 1.84 m) were examined. The shallow BB (L-0 = 0.56 m) was aerated at superficial gas velocities u(g) = 0.018, 0.031, and 0.038 m.s(-1), respectively. Both medium (L,, = 1.12 m) and deep (L-0 = 1.84 m) BBs were aerated only at u(g) = 0.038 m.s(-1) (churn-turbulent flow regime). It was found that the new graphical method is applicable only for a deep BB (L.D-c(-1) = 7.3). In that particular case, the difference between the experimental mass transfer time and the graphically determined one is reasonable (the maximum relative error is only 6.9%). Therefore, the new graphical method should he adopted for experimental determination of the mass transfer time in a deep BB. The new method is of practical importance because the industrial bubble columns operate with deep BBs.