Sulfonation of a low molecular weight linear alkyl benzene (LAB) commercial cut with SO3-air mixtures was conducted in a corrugated wall falling film reactor (CWFFR). The aim of the study was to compare the performance of this reactor with that of a conventional smooth wall falling film reactor (SWFFR) of the same length. The influence of parameters such as the SO3 to feed molar ratio, SO3-in-air concentration and geometry of the wall on the Klett color and active matter yield in the product was investigated. For low values of the SO3 to feed molar ratio, a better color and a significant increase in the active matter content in the product were obtained with the CWFFR. Results also suggest a possible competition between turbulence induced by the corrugated wall and stagnation also caused by the wall. (C) 2000 Elsevier Science S.A. All rights reserved.