The concentration and viscosity of the slurry are related to each other, and they have a unique importance in the case of industrial application of the slurry. It is well known that the fluidity of a coal-water slurry with a high coal concentration is largely affected by the nature of the dispersing agent. Therefore, there are good reasons for seeking an understanding of the adsorption behavior of the dispersants on the coal particle surfaces. The aim of this investigation is to determine the adsorption behavior of a non-ionic dispersant, polyoxyethlene sorbitan monooleate, on Turkish lignite samples. The effects of the dispersant concentration, temperature, time and pH on dispersant adsorption were investigated systematically. The results are also analyzed by a two level factorial design matrix to explain the effects of the parameters on the adsorption, and multilinear mathematical models representing the adsorption behavior of the dispersant used within the experimental conditions are proposed for each coal sample used. (C) 2002 Elsevier Science Ltd. All rights reserved.