The presence of potential determining ions (PDIs) in the injection water along with an optimum salinity is essential for enhanced oil recovery to achieve a more favourable water-wetness in carbonates. Smart waterflooding is a method of reducing the salinity and modifying the ionic chemistry of injection brine to increase water-wetness favourably leading to additional oil recovery. The process can be further optimized to achieve higher incremental oil recovery by selectively spiking the injection brine with PDIs such as SO42- Ca2+ and Mg2+. To understand the mechanisms, a detailed study was conducted to evaluate of the positive influence of major PDIs and salinity reduction on wettability alteration. Zeta potentiometric and coreflooding experiments were conducted using diluted- and smart-brines prepared by varying the composition of PDIs. Two corefloods were conducted through composite cores made up of core plugs arranged in series and results were analysed. The first coreflood used seawater and 100 times diluted-seawater and the second coreflood was conducted using smart brines. Finally, a reservoir simulation study was conducted to match and validate displacement results from both corefloods. Zeta potential and coreflooding experiments with diluted brines and smart brines gave positive results in that the zeta potential was found to be increasing with increasing dilution of SW. This finding was also corroborated by results from coreflooding in both secondary and tertiary modes of recovery. An incremental oil recovery of about ~28% was obtained by 1%dSW from both corefloods, and an increase in sulfate ion concentration in successive brines yielded about ~19.35% additional oil recovery. To validate the experimental results, a single porosity simulation model was used to history match the coreflooding data. The model provided a reasonable match with experimental results and showed that rock dissolution is an important mechanism by analysing the brine and mineral parameters. Other mechanisms discussed through integration of zeta potentiometric and coreflooding experiments are electric double layer (EDL) and surface ion exchange. A combination of these mechanisms is concluded to enhance oil recovery by smart waterflooding. The study demonstrates that injected brines with optimized salinity and concentration of PDIs can be effective in improving recovery by wettability alteration to more water-wet state.