The separation of CO2 from biogas to achieve vehicle/pipeline grade methane is an expensive step. Recently, PEI (polyethyleneimine) impregnated resins have been proposed and evaluated for CO2 separation from flue gases and air. However, its use in biogas upgrading and evaluation of the economic feasibility of such adsorbents have not been explored in detail. In this work, by modifying an inert polymeric resin (HP2MGL) using PEI, CO2 was separated from biogas. The sorbent exhibited the highest adsorption capacity of 2.7 mmolCO2/gads at 30% PEI loading, increasing to 2.9 mmolCO2/gads in the presence of moisture, and remained stable for up to five adsorption.desorption cycles. In situ DRIFTS studies showed that CO2 adsorption on PEI-impregnated sorbent is consistent with the zwitterion reaction mechanism, and the sorbent could be regenerated completely at 100 °C. The upgrading cost of biogas is primarily dominated by the operating cost of regeneration and the adsorbent cost. The economic feasibility analysis suggests that PEI-impregnated resin sorbent requires less capital and operating costs than conventional biogas upgrading technologies. Therefore, PEI-impregnated polymeric resins are promising for CO2 separation from biogas.