This paper presents the effect of surface tension of solution used as medium for the oil agglomeration of minerals. Naturally occurring hydrophobic and hydrophilic minerals are used in this study. It was determined that the oil agglomeration recoveries of these minerals decreased with decreasing solution surface tension and the oil agglomeration process of the mineral did not occur below a particular value of solution surface tension. The solution surface tension value at which oil agglomeration does not take place was defined as 'the critical solution surface tension for oil agglomeration, gamma (c-a)'. These critical solution surface tension values obtained for those hydrophobic minerals were close to their critical surface tension of wetting (gamma(c)) values. On the other hand, the gamma(c-a) values obtained for the hydrophilic minerals treated with surfactants were slightly higher than their gamma(c) values. For a successful oil agglomeration of a mineral, the solution surface tension value must be higher than the critical surface tension of oil agglomeration (gamma(c-a)). (c) 2004 Elsevier B.V. All rights reserved.