In this work a novel experimental technique for measuring local gas hold-up, interfacial area and bubble size distribution, in gas liquid systems is proposed. The technique is based on advanced Image Processing coupled with experimental set-ups typically available for Particle Image Velocimetry. A fluorescent dye dissolved in the liquid phase allows to identify in plane bubbles among all visible bubbles in the images. To this end, a suitable algorithm is proposed. The raw data so obtained are processed by previously developed statistical methods that result in a reliable reconstruction of actual dispersion properties. The technique is applied to the case of a gas-dispersed mechanically agitated vessel, and the data obtained arc presented and discussed. (C) 2013 Elsevier Ltd. All rights reserved.