In this paper, we report on the use of X-ray tomography to visualize and quantify the gas-liquid interfacial area in modular catalytic distillation packing elements. The calculation method is based on processing of tomographic images. It is validated by comparing specific surface area determined on dry packings (Mellapak (TM) 752Y and Katapak (TM) SP12) tomographic binary images (gas and solid) to values announced by manufacturers, based on geometrical considerations. These data agree fairly well. However, tomographic images show that the specific area is not distributed uniformly over the height of a packing element due to the presence of perforations in corrugated sheets and of wall wipers between the packing and the column wall. X-ray tomography is a unique technique to access to the spatial distribution of these geometrical details in a non-intrusive way. The method used to determine the specific surface area of dry packing is then applied to irrigated packing in order to determine the gas-liquid interfacial area. The axial distribution of the interfacial area is non-uniform and is correlated to the packing specific area. The maxima of the specific surface area correspond to the presence of wall wipers. The gas-liquid interfacial area averaged over the column length is determined. It increases logically with the liquid superficial velocity and slightly with the gas velocity. The effect of the gas velocity is however more pronounced when reaching loading point. (C) 2009 Elsevier Ltd. All rights reserved.