The development of nanotechnology has altered the petroleum sector. Nanotechnology has been tested in the field of exploration. Drilling, production and eventually increased oil recovery are all part of the process. In the case of enhanced oil recovery (EOR), nanoparticles (NPs) in form of nanofluids are regarded as the smart fluids used to displace residual oil from the reservoir. Improving the viscosity of the injected NPs facilitates the displacement of the crude oil. However, NP's sedimentation in the fluids has become a great challenge that renders the performances of NPs worthless. This work focuses on investigating the stability and viscosity of the composite nanofluids that incorporate the merger of silicon dioxide (SiO 2) and zinc oxide (ZnO) NPs. The nanocomposite was formed and supported by surfactants to improve the viscosity and sedimentation in comparison with its constituents. The results obtained have shown that the stability and viscosity of ZnO and SiO 2 NPs have increased by 37 and 43 , respectively, when ZnO/SiO 2 was used. Furthermore, upon introducing a nano-surfactant solution, the stability and viscosity increase to 54 and 44 , respectively. © 2022 Elsevier B.V.