Viscosimetry, tensiometry, and X-ray diffraction have been employed to determine physicochemical and structural properties of an Algerian asphaltene in solution. A new viscosity analysis scheme was adopted to extract information about the shape of the asphaltene aggregates, the solvation, and the inter-aggregate interactions. The average molecular weight (MW) was deduced by combining the surface tension and viscosity studies. The average MW of this asphaltene appears to be small in comparison with those measured by vapor pressure osmometry (VPO) but comparable with the recent results from mass spectroscopy, atomic force microscopy, and fluorescent spectroscopy. X-ray measurements show that asphaltene molecules aggregate, even in the neat phase, and an average aggregate is composed of 4−5 aromatic sheets. The viscosity study suggests that asphaltenes in toluene solutions behave in accordance with a spherical micellar model containing aggregated asphaltene molecules with a substantial amount of solvation.