The dissolution and dilution of asphaltenes in organic solvents was investigated using a microtwin-calorimeter at 25 degreesC. Quinoline, o-dichlorobenzene, 1-methylnaphthalene, tetralin, ethylbenzene, and toluene were used as solvents. Heats of solution were exothermic in all solvents and appeared to correlate with the solubility parameter of the solvents used, which suggested that dissolution is dominated by interactions between the asphaltene and solvent molecules. On the other hand, dilution of a concentrated asphaltene solution was endothermic, which could be attributed to dissociation of aggregates or micelles in solution.