After initial and secondary oil recovery up to 50% of the oil can be left behind in the reservoir. Various enhanced oil recovery (EOR) techniques can be applied to improve the recovery factor. Alkali, surfactant and polymer (ASP) flooding is a promising EOR method that is currently being explored. The main principle is using surfactant to reduce the interfacial tension between the water and oil phase to mobilize the oil which is trapped by capillary forces. The optimum surfactant formulation will generate a third phase “microemulsion”, which is a thermodynamically stable mixture of oil, brine and surfactant. This microemulsion can have undesirable properties such as a high apparent viscosity when it flows through the porous rock formations. The understanding of the structure and flow behaviour of this microemulsion phase is important for clarifying the mechanism of ASP EOR flooding.