The phase behaviors of pseudo ternary mixtures of water/Tween 80/Span 80/Hexane were studied by constructing a series of phase equilibriums at 30°C. After the phases underwent separation by centrifugation, birefringence was observed under crossed polarized light. The results showed that the mixtures of Tween 80 and Span 80 were able to solubilise in water and hexane by forming association structures like micro-emulsion and liquid crystalline phases. In the attempt to formulate stable O/W emulsions; several compositions were selected from the phase equilibriums to compare their stability. The extracted essential oil of citrus hystrix was then incorporated into the emulsions as additive and fragrance. From the stability test, the results showed that the emulsions, in which the percentage of Tween 80 that was much higher than the Span 80, were more stable.