The L-phase of the three-component system water - sodium octanoate -butanol extends over a large composition range. It is well known that micellar aggregates exist in the water rich part (the L1part) and inverse micellar aggregates in the butanol rich part (the L2part). The mechanism for the change from a continuous water medium to a continuous butanol medium in the middle part is of fundamental interest. The properties of the L-phase were studied by density, refractive index, ultracentrifugation, electromotive force and conductivity measurements. This investigation indicates in which regions aggregation occurs as well as the changes in aggregate and medium structure which take place with increased butanol concentration.