Surface tension is one of the most important factors in a flotation process, normally being understood to mean surface tension at the pulp surface. In most cases this is enough, but when we try to process materials which have low surface energies, we also have to take into account the surface tension between the air bubbles and the liquid (water) in the flotation cell. This paper reports preliminary study results on this subject. (C) 2003 Elsevier Ltd. All rights reserved.