Many carbonate oil fields are known to be oil-wet, which makes production more difficult. Enhanced oil recovery methods have been developed in the past to reduce interfacial tension (IFT) and improve displacement efficiency by injecting higher viscosity solutions. This work focused on the production of ZnO/SiO2 nanocomposite (NC) that is designed to reduce IFT during water-flooding of an oil-wet rock sample from the Upper Qamchoqa carbonate formation. A natural polymer was used as a mobility modifying agent to increase oil recovery. In addition, the effects of water salinity, NC concentration, temperature, and pressure have been analyzed to determine potential improvement on the performance of the stated chemical additives to the injected fluids. ZnO/SiO2/xanthan NC was prepared in a simple, economical, and importantly, green way using the pomegranate seed extract and characterized with scanning electron microscopy, transmission electron microscopy, and Xray diffraction. The potential effect of the polymeric ZnO/SiO2 nanofluid on IFT reduction was studied. Core-flooding was carried out to investigate the effects of this IFT reduction on relative permeability curves. The results show that the nanofluid with 2000 ppm NC concentration at high temperature and high pressure significantly reduced the IFT, by about 93.6%, from 31.8 to 2.016 mN/m compared with seawater injection, also increasing the oil recovery by about 19.28% from 46.96 to 66.24%, with high shifting of the relative permeability curve to the right. The derived NC is very promising as a chemical for enhanced oil recovery.