The surfaces of three Australian coals varying widely in coal type (Collie, Wongawilli and Norwich Park) have been modified by adsorption of three surfactants (sodium dodecyl sulphate, cetyl trimethylammonium bromide and Teric GI2A8). The mechanism and impact of the surfactant adsorption has been explored by correlating three chemical characterisation techniques. Changes in coal surface hydrophobicity were assessed using contact angle measurements at the coal/water interface. Adsorption of surfactants did not increase the surface hydrophobicity for the lowest rank coal, however appreciable changes in contact angle were measured as the rank of the coal increased. As the coal rank decreased, the surfactant adsorption densities increased far all three surfactants under investigation. The largest variation in zeta potential resulting from addition of surfactants was seen for the higher rank coals. The results from this study have allowed a possible surfactant adsorption model to be postulated. (C) 2001 Elsevier Science Ltd. All rights reserved.