The gas-liquid mass transfer of H-2 and CO in a high temperature and high-pressure three-phase slurry bubble column reactor is studied. The gas-liquid volumetric mass transfer coefficients k(L)a are obtained by measuring the dissolution rate of H-2 and CO. The influences of the main operation conditions, such as temperature, pressure, superficial gas velocity and solid concentration, are studied systematically. Two empirical correlations are proposed to predict k(L)a values for H-2 and CO in liquid paraffin/solid particles slurry bubble column reactors.