This paper deals with the relation between the rheological properties and the structure of waxy crude oils cooled in quiescent conditions and under flow. In the dynamic regime, measurements were performed on gels cooled slowly in order to allow paraffin crystallisation in equilibrium. The amounts of crystalline material vs. temperature were measured independently by differential scanning calorimetry or NMR and the morphology was observed by transmission electron microscopy. The relation between the shear moduli and the crystal content was established and analysed in the framework of colloidal gels with a fractal structure. Besides, a series of experiments is presented, with various shearing protocols, leading the oils into different states: steady viscosities were measured under various shear rates and at constant temperatures, cooling was performed under constant shear stresses. Creep experiments leading to fracturing of the gels and dynamic measurements which allow to follow the time evolution of cooled crude oils, after extensive shearing, are shown. The various types of experiments were also interpreted in the framework of the colloidal suspensions with a fractal structure. The rheological modifications were ascribed to changes of morphology of the clusters made of aggregating particles, which are the small crystallites of paraffins, in agreement with transmission electron microscopy observations. (C) 2004 Elsevier Ltd. All rights reserved.