This paper relates to our three-dimensional time-resolved experimental investigations into the flow patterns in flat, rectangular air-water bubble columns. Flat, rectangular bubble columns (the so-called "two-dimensional" or "2D" design) have been part of many experimental and theoretical studies, and our present investigations shed more light on the flow patterns in these systems through velocity measurement profiles in three-dimensions, reported as a function of operating conditions and aspect ratio of column. The investigations have been conducted with the Radioactive Particle Tracking technique (RPT), by following a neutrally buoyant radioactive particle with the help of scintillation detectors, and subsequently subjecting the measured trace to ensemble-averaging data treatment techniques. The investigations reveal quantitative measurements of the flow and circulation patterns which have not so far been reported, and also provide unique validation data for the theoretical modeler. (C) 2013 Elsevier Ltd. All rights reserved.