In order to study the effect of frothers on the size of bubbles, experiments were carried out using single- and multi-hole spargers and a flotation cell. It was found that the size of bubbles strongly depends on frother concentration only when multi-hole spargers are utilized (or when measured in a flotation cell). At low frother concentrations (C < CCC), the bubble size is much larger, indicating coalescence as a main mechanism determining the size. Coalescence can be prevented at frother concentrations exceeding the critical coalescence concentration (CCC). The foamability tests indicate that stability of foams under dynamic conditions is determined by bubble coalescence. (C) 2002 Elsevier Science B.V. All rights reserved.