Polar fractions of Hassi-Messaoud asphaltenes were obtained by two different extraction/precipitation procedures. Properties of these fractions were studied using elemental analysis, LDI-TOF mass spectroscopy, and solid state C-13 NMR. The aggregation and the flocculation onset of polar fractions were determined. It was demonstrated that the most polar fraction of asphaltenes that is soluble in highly polar solvents, such as N-methyl pyrrolidone and nonsoluble in mildly polar or nonpolar solvents is composed of small molecules, containing a high oxygen ratio. This fraction plays an important role in asphaltene aggregate formation. The understanding of this role would be helpful for designing new antiflocculation agents.