The distribution of axial solid concentration was investigated experimentally and theoretically in tapered and cylindrical slurry bubble columns using air as the gas phase, tap water as the liquid phase and quartz sands as the solid phase. Based on the sedimentation-dispersion model commonly used in cylindrical columns, a mathematical model was presented to predict the solid concentration distribution in the tapered column. Superficial gas velocities up to 0.28 m/s, slurry concentrations up to 159 kg(solid)/m(3)(slurry), and static slurry height from 1.6 to 2.7 m were measured. The axial solid concentration distribution becomes uniform with an increase in superficial gas velocity or average solid concentration and with a decrease in particle diameter or static slurry height. The experiments were carried out in the cylindrical column under similar operating conditions to compare differences in the axial solid distribution measured in cylindrical and tapered columns. The results showed that the tapered column provides a more uniform profile of axial solid concentration than the cylindrical column. An empirical correlation for Peclet number was developed using dimensional analysis, which can predict the axial solid concentration distribution in tapered columns.