Two types of water-in-oil (w/o) microemulsions : anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB) have been studied at various temperatures (25-35°) as a function of alkyl chain-length of co-surfactant (n-alkanols, C 4 OH-C 8 OH) and oil (n-alkanes, C 5 H-C 7 H). The free energy of transfer of co-surfactant from the continuous oil phase to the interfacial region (ΔG 0 5 ) has been reported and the adsorption free energy per methylene group of the alkanols (ΔG 0 s , a l k a n o l /CH 2 ) has been computed. With increase in the water content the appearance of mieroemulsion systems changed from a clear solution to bluish which finally became turbid. The transitions were identified on the basis of specific resistance measurements. A significant change in specific resistance was observed at the transitions. The critical n w a t e r /n o i l ratio (V c ) where the microemulsion is about to breakdown, was calculated with the help of viscosity measurements.