A critical review is presented on the mass transfer characteristics of gas¿liquid slurry reactors. The recent findings on the influence of the presence of solid particles on the following mass transfer parameters in slurry reactors are discussed: volumetric gas¿liquid mass transfer coefficients (kLa, kGa), liquid-side mass transfer coefficients (kL and kS) and specific gas¿slurry contact area (a). The second part of this paper reviews the recent progress in our knowledge and understanding of the enhancement of gas¿slurry mass transfer due to the presence of solids. Five different cases are distinguished, i.e. ¿ enhanced mass transfer by physical adsorption on small particles. ¿ enhanced mass transfer by fast homogeneous reactions in the slurry, due to inert particles, ¿ enhanced mass transfer by homogenous reaction in the liquid with dissolving particles, ¿ enhanced mass transfer due to reactive particles and ¿ enhanced mass transfer due to catalytic particles in heterogeneous reactive systems. Prospective areas for additional research are identified.