AbstractFirst CO2-EOR application to the offshore oil field in Vietnam has been investigated through an international joint study scheme between Japan and Vietnam since 2007 and a preliminary study outcome indicated feasibility to some extent. To reduce and mitigate uncertainties/risks in the field scale EOR implementation, a CO2-EOR pilot test was executed in Vietnam offshore oil field in 2011.The test was conducted as a single-well Huff ‘n’ Puff. CO2 was injected into the well and the well was flowed after soaking. In order to confirm the CO2-EOR effect the following items were monitored during the test: 1)CO2 Injection Performance2)Real Time Bottom-hole Pressure/Temperature3)Oil/Gas/Water/CO2 Production Performance4)Fluids' Saturation Change before and after CO2 Injection5)Produced Fluid Property & Composition on-siteOver 100 tons of CO2 were successfully injected into the well. Bottom-hole pressure was kept higher than MMP (Minimum Miscibility Pressure) during the injection period, thus miscible condition was considered to be achieved in the reservoir at least near the wellbore. The vertical contrast of CO2 injectivity and oil saturation change in the reservoir were confirmed by saturation logs and production logs. Clear increment of oil rate, reduction of water cut and oil composition change were observed after CO2 injection. Simulation study for matching pilot test performance was carried out and its result was in good agreement with the monitored data.