The L phase of the ternary CTAB/benzyl alcohol/water system that extends from the water corner to the alcohol corner was studied by the sound velocity method which indicated variations in velocity when the aggregate structure changed from normal micelles in water to reverse micelles in the alcohol corner of the phase diagram. From these results it was concluded that the transition from normal to reverse micelles takes place while passing through two different bicontinuous regions, one of them with alcohol micro domains dispersed in water and the other one as a bicontinuous reverse region with the predominance of the water domains dispersed in alcohol.