Hydrophilic-lipophilic deviation (HLD) concept describes interaction of surfactant, oil, and water in liquid formulations. Within the framework of HLD, this study investigated the behavior of microemulsion consisting of fragrance/essential oil mixtures and surfactants mixture commonly found in consumer products. Strong non-ideal mixing behavior was seen in oil mixtures of fragrance raw materials. A simple non-ideal relationship was proposed to account for the non-ideality of oil mixture of dissimilar properties. With 95% confidence, the error of the predicted optimum salinity (or phase inversion point) is between 0.70 to 1.68 g/100 mL NaCl in mixtures of complex commercial fragrance and octane. Mixing behavior was also evaluated in a ternary surfactants system consisting of sodium laureth sulfate (SLES), cocamidopropyl betaine (CAPB), and decyl glucoside (APG). Within a reasonable tolerance, the ideal mixing rule can be practically applied for such complex surfactant mixtures. Extension of HLD in mixture systems provides practical benefits in product development.