Reverse micellar (L2) phase in (TTAB+pentanol)/water/n-octane, mapped by using optical method, was investigated by preparing mixtures of 30%, 40%, 50%, 60% and 70% by weight of (TTAB+pentanol)(1:1) in n-octane. Positron annihilation studies were performed in these mixtures as a function of water concentration. Around water concentrations of 13.8%, 11.1%, 8.4%, 7.9% and 9.1% respectively, ortho-positronium pick-off lifetime tau 3 shows oscillatory behaviour whereas positronium formation I3 exhibits abrupt change. These changes have been attributed to the setting in of bicontinuous phase. Electrical conductivity measurements support these results. Positron annihilation technique can thus distinguish between droplet-like and bicontinuous structures in L2 phase.