A wire-mesh tomography device was used to study the liquid saturation at 78 points covering the cross-sectional area of a 0.30 m diameter trickle bed reactor. Measurements in the pulsing flow near the transition were done for glass beads and alumina cylinders using air and water as fluids. Local liquid saturation measurements allow identification of flow regime and pulse frequency for each of the 78 points considered. To the best of the authors' knowledge this is the first time that such local measurements are done for the complete sectional area of a trickle bed reactor. Flow rate conditions at which different flow regimes coexist at the same horizontal plane of the column were identified. A remarkable influence of the initial liquid distribution on the observed flow regime was also observed. (C) 2007 Elsevier Ltd. All rights reserved.