The phase diagram of a isopropyl myristate (IPM), water, leckhin/decyl polyglucoside (1:1), butanol mixture was constructed and the region of the o/w microemulsion was examinated. The realm of existence of this system was also investigated employing eight different, linear and branched short-chained alcohols as cosurfactants. The alcohol contribute to the extention of the microemulsion domain was explained in terms of lipophilicity and solubility. Moreover, the role of the cosurfactant was examined in a relationship study where the amount required to form the microemulsion of a series of twenty alcohols was related to a set of new structural descriptors of these molecules, the WHIM indices.