The global gas-liquid-solid volumetric mass-transfer coefficient K(L)a of a catalytic multiphase microstructured film contactor, featuring 5 mu m dimensions, a 155 mu m liquid film thickness, and a 15 mu m thin catalytic layer is determined, using the very fast hydrogenation of a-methylstyrene with a Pd/gamma-alumina catalyst. The volumetric mass-transfer coefficients measured experimentally fall in the range 0.8-1.6 s(-1) above that predicted by the film model and those obtained from a CFD (3-D model) simulation, and from an analytical solution. (c) 2006 American Institute of Chemical Engineers