During the past decade, several experimental studies have confirmed that Smart Water injection in sandstone reservoirs could significantly improve oil recovery. Most reported enhanced oil recovery effects are described as wettability alteration creating changes in capillary forces improving the displacement efficiency. Spontaneous imbibition (SI) is one of the main recovery mechanisms in porous media, where positive capillary pressure causes brine invasion into fractional and water-wet oil-containing pores. Numerical models for fluid flow in reservoirs are based on Darcy's law, describing the viscous forces involved, however not accounting for oil displacement by spontaneous imbibition of water. To demonstrate the importance of capillary forces in oil displacement by wettability alteration induced by Smart Water injection, a series of experimental low-rate oil recovery tests were performed. A low flooding rate was chosen to facilitate wettability alteration and allow capillary forces to contribute in the oil production without the influence of high viscous forces. Only one low-permeability and heterogeneous reservoir sandstone core plug was used in all tests. Before each experiment, the core went through optimized cleaning and restoration procedures to reproduce the same initial core wettability, thus minimizing any influences of varying initial wettability. Both viscous flooding (VF) and SI oil recovery experiments were conducted using different injection brines, and oil recovery results using formation water (FW) and modified seawater (mSW) were compared with secondary and tertiary low-salinity (LS) Smart Water injection. The experimental results confirmed that core wettability and capillary forces have a significant effect on ultimate oil recoveries, both in spontaneous imbibition and viscous flooding experiments. In this particular low-permeability sandstone, the capillary force-driven oil recovery by SI was as high as that from the low-rate VF experiments. The results confirm the importance of capillary forces in oil recovery processes from low-permeable and heterogeneous rock. Additionally, it was observed that LS brine was able to induce wettability alteration toward more water-wet conditions and significantly improve the ultimate oil recovery, compared to FW and mSW brines.