The main objective of this study was to provide novel insights into the mechanism of asphaltene aggregation in toluene/heptane (Heptol) solutions and the effect of alkylphenols on asphaltene dispersion through the integration of advanced experimental and modeling methods. High-resolution transmission electron microscope (HRTEM) images revealed that the onset of asphaltene flocculation occurs near a toluene/heptane volume ratio of 70:30 and that flocculates are well below 1 μm in size. To assess the impact of alkylphenols on asphaltene aggregation, octylphenol (OP) and dodecylphenol (DP) were evaluated by impedance analysis based on their ability to delay the precipitation onset and to reduce the size of nonflocculated asphaltene aggregates in 80:20 toluene/heptane solutions. Although a longer dispersant chain length did not affect the precipitation onset, it reduced the size of the aggregates. Molecular dynamics simulations were then performed to understand the mechanism of interaction between a model asphaltene and OP in heptane. OP molecules saturated the H-bonding sites of asphaltenes and prevented them from interacting laterally between themselves. This explained why OP favored the formation of flocculates with filamentary rather than globular structures, which were clearly observed by HRTEM. Although OP proved to be an effective dispersant, its effectiveness was hindered by its self-association and the fact that it interacted at the periphery of asphaltenes, leaving their aromatic cores uncovered.