The field performance of hydraulic oils depends on factors such as the viscosity index (VI), flash point (FP), pour point (PP), and demulsibility. A hydraulic oil formulation was performed by applying a multiresponse optimization, for which the PP was minimized, the FP, demulsibility, and VI were maximized. The range of viscosities at 40 and 100 °C was selected according to the International Organization for Standardization (ISO) viscosity grade for hydraulic oil. The experiments were accomplished according to an extreme vertices mixture design using solvent neutral-100 (SN-100) and SN-500 as major components and polyisobutene (PIB) as minor component. The results shows that the optimum formulation consisted of 37.5% SN-100, 60% SN-500, and 2.5% PIB, and the values of FP, PP, VI, demulsibility at 30 mins and viscosities at 40 and 100 °C were equal to 227 °C, −6 °C, 107.5, 28/2012/40, 67.3 cS, and 9 cS, respectively.