This article presents an experimental study of comparing different carbon dioxide (CO 2) injection mode for a reservoir in Malaysia (Alpha X Reservoir). The main objective is to determine the most technically optimum miscible CO 2 injection mode or strategy for this field. Using coreflood equipment, miscible CO 2 displacements were conducted on four berea core plugs that have been saturated with crude oil from the reservoir. Almost 2 PV of water and/or gas were injected into the cores with different modes. The experiments were conducted at the minimum miscibility pressure of the crude oil to ensure that CO 2 is fully miscible with the oil. The results indicate that the simultaneous gas injection yields the highest incremental oil recovery, about 28 oil originally in place. Based on the calculation of utilization factor and tertiary recovery factor for each injection mode, it was confirmed that simultaneous gas injection is the best injection mode for Alpha X reservoir. It gives the highest recovery per unit of CO 2 injected and utilizes relatively the least volume of CO 2 to produce a unit of oil. © 2012 Copyright Taylor and Francis Group, LLC.