Accords to the Montreal Protocol, CFC-113, known to be an ozone-depleting substrate, is now being strictly limited in use as a cleaning solvent especially in the eletronic industry. Therefore, the development of alternative cleaners to CFC-113 is indispensable. Previous research in our group has shown that the removal of representative flux residues using aqueous nonionic surfactant solutions is closed related to the formation of a miroemulsion. In the present investigation, hte effect of cosurfactant content on the phase behavior in systems containing NP series nonionic surfactant, water, D-Limonone is examined. The emphasis here is on the effect of cosurfactant on the microemulsion phase behavior. Also presented are solubilization experimental results using three different types of microemulsions. Interfacial tension data are also presented to provide further information on the effect of cosurfactant.