The influence that 1,3-butyleneglycol incorporated as polar cosolvent in the aqueous phase determine on the O/ W micromulsion region of the classical system water/ sodium dodecyl sulfate/ pentanol/ heptane, has been studied. Phase diagrams corresponding to aqueous phases made of water/ butyleneglycol in ratios 907sol; 10 and 75/ 25 are compared with the typical system with water.The resulting increase on the OAV microemulsion region for the systems including the glycol, provides a security margin to prepare such compositions with respect to the narrow channel of solubility described for the conventional system. Although the presence of butyleneglycol lead to a shift in the optimal ratio between the aqueous phase and SDS from the 85/ 15 described for the typical system to higher proportions in surfactant, the simplicity of preparation of such O/W microemulsions could compensate the higher amount of SDS required