CO2 emissions can be reduced by storing it in underground geologic formations such as coal seams, mature or depleted hydrocarbon reservoirs and deep saline aquifers. The combination of carbon dioxide enhanced oil recovery and permanent CO2 storage in mature oil reservoirs has the advantage to project economics. In this research, CO2 storage capacity of a CO2 flooded mature oil reservoir was estimated and the contribution of the CO2 injection to oil recovery was determined by conducting a full-field compositional simulation study. Detailed reservoir characterization study was done to build the geologic model. Reservoir fluid was characterized by sticking laboratory observations. 3-Parameter Peng Robinson EOS was used. Fugacity equilibration method was used to calculate CO2 partitioning between oil and gas. Performing the study in a CO2 flooded reservoir increased the reliability of the predictions by accurately history matching the 30 years of production and 10 years of CO2 and water injection periods. Simulation results showed that applying the CO2 storage project in an almost depleted oil field should increase the field's life and high amount of CO2 should be sequestered. Most of the sequestered CO2 was trapped by structural and stratigraphic trapping mechanism and contribution of solubility trapping mechanism is lower.