The purpose of this study was to investigate the effect of process parameters including silica nanoparticle (NP) concentration, biosurfactant (BS) concentration, and salinity as well as their synergistic effects on oil recovery in simultaneous flooding. Additionally, the effect of NP morphology (in the BS-NP solution) on oil recovery was investigated in this research. Micromodel flooding tests were designed with a central composite design (CCD) and carried out using BS and spherical silica NPs. The results showed that there is a positive synergistic effect between BS and silica NPs to shift the wettability to the water-wet condition and decrease interfacial tension (IFT), resulting in improved oil recovery. Indeed, the maximum oil recovery was obtained at an optimum salt concentration. Several micromodel tests were then carried out with BS and different-shaped NPs at the optimum point predicted by a mathematical model to study the effect of NP morphology on oil recovery. The results showed that minimum IFT of 1.85 mN m⁻¹ and the most reduction in the glass contact angle of 92.8% could be achieved by the BS-spherical NP solution as compared to those of the BS-non spherical NP solutions, which led to the highest oil recovery of 53.4%. The better performance of spherical NPs was attributed to the higher uniformity, which resulted in better distribution and more effective interactions with crude oil components. The results of core flooding tests showed that the BS-spherical NP solution yielded 26.1% final oil recovery after brine flooding. In addition, the BS-NP solution was more effective in wettability alteration of an oil-wet carbonate rock compared with the BS solution. It was deduced that the main mechanisms involved in oil recovery improvement were wettability alteration to the water-wet state, IFT reduction, and mobility ratio improvement.