Several studies have reported that the viscosity profile of nanofluids has a similar trend to electrolytes. This behavior is attributed to the complex interactions of the ions of nanoparticles (NPs) with the ions of aqueous solutions. Recently, laboratory experiments have shown that nanofluids are suitable candidates for enhanced oil recovery in different reservoirs. The improvement in oil recovery during nanofluid injection is attributed to the wettability alteration, interfacial tension reduction, and viscosity modification. Low salinity water and surfactants are used to stabilize and prevent the aggregation of NPs, which are injected into the reservoir. However, the interactions between the reservoir/injected fluids with NPs alter the properties of the fluid. The complex interactions among the ions present in the solutions of NPs, surfactants, and electrolytes (NSE) that result in the viscosity modification are not completely understood. Therefore, this work presents a detailed study on the complex interactions existing between the ions of NPs and other ions of aqueous solution present in the reservoir fluid using the dynamic light scattering, transmission electron microscopy, and Fourier transform infrared spectroscopy techniques to understand the viscosity behavior of NSE solutions. The viscosity profile of NSE solutions with increasing concentration of NPs has the same trend as aqueous solutions, while that with increasing concentration of the sodium dodecyl sulfate surfactant behaves like spherical particles. The explained mechanisms behind the viscosity behavior of NSE solutions in this study can improve the optimization design for nanofluid injection into the reservoir.