Using CO oxidation in a wall-coated tubular reactor, the enhancement of radial mass transfer by a static mixer was investigated. Experiments were conducted at various flow rates, CO concentrations and temperatures. Flow rates were chosen such that the flow remains in the laminar regime. Several effects were observed: light-off occurred at higher temperatures for higher flow rates and higher CO concentrations. Lower conversions were obtained for higher flow rates. In general, measured conversions were higher with the static mixer, compared to an empty tube under mass-transfer limited conditions. An expression for the Sherwood number, Sh = 2 + 0.059Re, was calculated for the system with static mixers. Our study demonstrates that the performance of wall-coated reactors can be significantly enhanced using static mixers. This reactor may be a new tool for reaction engineers, e.g., to replace catalyst-pellet-filled tubes in multi-tubular reactors to suppress hot-spot formation or for heterogeneously catalyzed viscous liquid-phase reactions. (C) 2003 Elsevier Science Ltd. All rights reserved.