The mechanism of action of additives that control the sedimentation of paraffin crystals after their crystallization in model diesel oil has been studied by means of a new experimental approach. The chemical analysis of the crystals and detailed measurements of the sedimentation phenomenon give new insights into this complex process. Thus, the wax antisettling additives used for preventing wax crystal sedimentation adsorb at the surfaces of wax particles and provide them with enhanced colloidal stability. The settling rate is not related to the size of the crystals or the viscosity of the liquid medium, but to the ability of the additives to prevent the aggregation of wax crystals. The reported methodology makes it possible to investigate the fundamental mechanisms, but also to evaluate structure-activity relationships of the various additives used in the petroleum industry. (C) 2003 Elsevier Inc. All rights reserved.