A molecular simulation model to study the mechanism for asphaltene aggregation is presented. Four species were selected, obtained from structural analysis of asphaltenes from the oil extracted from Castilla oil field, in Colombia. Energetic contributions to the aggregation process for each species were studied, and the solubility parameter was evaluated. Finally, the aggregation process between different species was studied in order to determine the tendency of the molecules towards self-association. Results show that for all species, aggregation state is energetically favorable; also, both Van der Waals interactions and electrostatic forces contribute equally to the aggregation process. It was also found that the molecular structure of the substances has a big influence on the manner in which asphaltenes aggregate. For continental structures, long ramifications cause a physical obstacle for aggregation. On the other hand, the molecular flexibility associated with archipelago structures enables the aggregation with other species, but somehow hinders the process of self-association. The solubility parameter for all four substances was within the range established by literature.