A large number of producing fields in Malaysia are already entering maturing stage for primary and/or secondary depletion with declining oil rates and increasing water cut and gas-oil-ratio trend. As of 2003, the average oil recovery factor for the producing field is 36.8. This means that there is still substantial amount of the remaining oil-in-place that could potentially be recovered through tertiary recovery or enhanced oil recovery (EOR). Carbon dioxide (CO2) miscible flooding has been identified to be the most amenable EOR process for these fields. However, to fully optimize the oil recovery from the process, the most effective injection mode must be determined. This paper presents a study of the effect of various CO2 injection modes on miscible flood performance for a reservoir in Malaysia. Using a black-oil numerical simulator, four injection techniques; continuous, simultaneous water and gas (SWAG), water alternate gas (WAG) and hybrid WAG; were simulated on the reservoir. From the results of thesimulations, the respective optimum injection modes for our case study reservoir were established. Comparing all the various optimum CO2 injection modes, SWAG injection with a CO2 injection rate of 15,000 Mscf/d and SWAG ratio of 1:1 is the most efficient recovery method for our reservoir.