In this work, X-ray tomography is used to analyse the influence of liquid-phase viscosity on liquid flow in a column filled with MellapakPlus 752.Y structured packing. Tomographic measurements are performed at various column heights for different liquid flow rates. Water and glycerine aqueous solutions are used as working liquids in order to quantify the influence of liquid viscosity on hydrodynamic characteristics, such as liquid hold-up and gas-liquid interfacial area. These grow with both increasing liquid flow rate and with increasing liquid viscosity. In all cases, the measured quantities show fluctuating axial profiles. Furthermore, tomographic images are used to identify different liquid flow patterns (films, contact-point liquid, flooded regions) inside the irrigated column. A method based on a morphological analysis is proposed to determine the fraction of liquid within each flow pattern depending on flow rate and liquid viscosity. (C) 2013 Elsevier Ltd. All rights reserved.