This paper presents an indirect method for determining the local gas holdup in the collection zone of flotation machines. The method includes a linear model to describe the gas holdup as a function of the superficial gas velocity and the percent area, defined as the 2D area fraction occupied by bubbles in binary images. Such images were recorded using a bubble viewer. More than 250 images of bubbles were processed to obtain suitable percent area estimations. The ability of the model to describe local gas holdup was tested at laboratory and industrial scale. The latter included self-aerated and forced-air mechanical cells from 8.5 m(3) to 300 m(3) and industrial columns from 42 m(3) to 160 m(3). The model was able to estimate the gas holdup ranging from 2.5% to 15% in laboratory and from 6.0% to 21.0% in industrial machines. As a result, a database of industrial gas holdup is presented, which includes 8 copper concentrators. The proposed methodology is a promising tool for gas dispersion characterization using a unique measurement system. (C) 2016 Elsevier Ltd. All rights reserved.