The volumetric mass transfer coefficient k(L)a in a 0.1 m-diameter bubble column was studied for an air-slurry system. A C-9-C-11 n-paraffin oil was employed as the liquid phase with fine alumina catalyst carrier particles used as the solid phase. The n-paraffin oil had properties similar to those of the liquid phase in a commercial Fischer-Tropsch reactor under reaction conditions. The superficial gas velocity U-G was varied in the range of 0.01 to 0.8 m/s, spanning both the homogeneous and heterogeneous flow regimes. The slurry concentration epsilon(s) ranged from 0 to 0.5. The experimental results obtained show that the gas hold-up epsilon(G) decreases with an increase in slurry concentration, with this decrease being most significant when epsilon(s) < 0.2. k(L)a/epsilon(G) was found to be practically independent of the superficial gas velocity when U-G > 0.1 m/s is taking on values predominantly between 0.4 and 0.6 s(-1) when epsilon(s) = 0.1 to 0.4, and 0.29 s(-1), when epsilon(s) = 0.5. This study provides a practical means for estimating the volumetric mass transfer coefficient kLa in an industrial-size bubble column slurry reactor, with a particular focus on the Fischer-Tropsch process as well as high gas velocities and high slurry concentrations.