One of the more interesting recent topics in flotation modelling is the association between the fraction of air that overflows to the concentrate as unbroken bubbles (air recovery, a) and concentrate recovery. This paper analyses several models to estimate air recovery. These models were tested using experimental data obtained with a laboratory flotation column (2 m high; 0.095 m diam.), which was used to float sphalerite. Predictions from these models were compared with the results obtained by image analysis. The aim of this last technique was to have a reference measurement, quantifying by visual detection (manual method) the bubbles bursting on the surface. Based on the experimental results, the best models were identified. This kind of comparison is valuable for simulator developers. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.