Hybrid enhanced oil recovery (EOR) as polymer-assisted carbonated waterflood (PCWF) improves mobilities of both aqueous and oleic phases. The process introduces synergetic effect modifying reservoir wettability and fluids’ viscosity. These effects are the results of polymer rheology, geochemical reactions, and interphase transport of CO2 in crude oil/brine/mineral system. In this study, its performance is compared to waterflood, polymer flood, and carbonated waterflood. Firstly, polymer injection of PCWF raises the viscosity of aqueous solution over 4 cp despite of chemical and mechanical degradations. Secondly, PCWF contributes to considerable calcite dissolution increasing molality of Ca2+ by 400%. It triples equivalent fraction of Ca2+ and the reservoir is modified toward more water-wet condition. Lastly, PCWF allows CO2 to be transferred from aqueous solution to oleic phase. This transport reduces oil viscosity with 8% while pressurized system by polymer injection viscofies oil. As a result, PCWF recovers additional oil with 14.5%, 9.5%, and 2% over waterflood, polymer flood, and carbonated waterflood after 1.5 pore volume injection. Despite of the synergetic effects, PCWF requires operating cost to consume polymer and CO2. To improve oil production and economic efficiency of PCWF, robust optimization with multiple heterogeneous permeable fields is performed. Optimum injection designs of PCWF increases net present value with 36% over waterflood.