The gas holdup, epsilon and volumetric mass transfer coefficient, k(L)a, were measured in a 0.051 m diameter glass column with ethanol as the liquid phase and cobalt catalyst as the solid phase in concentrations of 1.0 and 3.8 vol.-%. The superficial gas velocity U was varied in the range from 0 to 0.11 m/s, spanning both the homogeneous and heterogeneous flow regimes. Experimental results show that increasing catalyst concentration decreases the gas holdup to a significant extent. The volumetric mass transfer coefficient, k(L)a, closely follows the trend in gas holdup. Above a superficial gas velocity of 0.04 m/s the value of k(L)a/epsilon was found to be practically independent of slurry concentration and the gas velocity U; the value of this parameter is found to be about 0.45 s(-1). Our studies provide a simple method for the estimation of kLa in industrial-size bubble column slurry reactors.