One of the most important solvent physical parameters for aggregation is the cohesive energy density (CED), for it gives an idea of the structured state of the solvent. Nevertheless, our studies on the behavior of catanionic amphiphiles in nonaqueous solvents demonstrated that in order to obtain objects the dielectric constant of the solvent was also a critical parameter, as a too high value of the dielectric constant caused the dissociation of the catanionic ion pair, leading to the separation of the two oppositely charged surfactants composing the catanionic amphiphiles, and then more likely to form small objects such as micelles rather than vesicles. In the case of our glucose-derived catanionic surfactants, vesicles could be obtained in pure water, in glycerol/water mixtures, and in water/formamide mixtures up to a certain ratio of formamide. Above a formamide volume fraction of 0.7, only micelles were formed.