The hydrodynamics and mass-transfer characteristics of monolith loop reactors, with upflow of gas and liquid phases through the channels, have been investigated and compared with conventional internal airlift reactor and bubble column configurations. The volumetric mass-transfer-coefficient per unit volume of dispersed gas bubbles, k(L)a/epsilon(G), is significantly higher for monolith reactors than for airlift and bubble columns. This improvement is due to the superior mass-transfer characteristics of Taylor flow in narrow capillaries. Application of low-frequency vibrations has the effect of significantly improving k(L)a/epsilon(G) for all reactor configurations studied. For monoliths, vibrations also have the additional beneficial effect of improving the gas-liquid distribution through the channels. (C) 2004 Elsevier Ltd. All rights reserved.