The hydrodynamics and mass transfer characteristics of a monolith loop reactor, 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, k(L)a, is 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. In order to gain further insight into the mass transfer from Taylor bubbles, experimental results are presented on the unit cell lengths and the Taylor bubble rise velocity. (C) 2004 Elsevier B.V. All rights reserved.