Abstract: This study presents the behavior of surfactant in microemulsion during chemical EOR process. Previous work performed on microemulsion phase behavior illustrated type III as the most suitable for achieving ultra low Interfacial Tension, assuming all surfactants to be soluble within the middle phase microemulsion. Based on our experimental results, this assumption was proven to be invalid. Phase behavior experiments were conducted at various salinity increments to generate gel and liquid crystal free microemulsion using surfactant and co-solvent. Different phases of type III microemulsion were then separated and analyzed for the surfactant partition distribution in the aqueous and microemulsion phase. The surfactant concentration in each phase was monitored by UV-visible spectroscopy. Observations from experimental results indicated that more than 31% of total surfactant was left behind in the aqueous phase rather than going entirely into microemulsion phase. Hence, the general statement that assumes all surfactant to be soluble in the microemulsion phase is not valid for all cases.