CO2 sequestrated in deep geological formations can be in gaseous, supercritical or liquid state, depending on subsurface pressure and temperature. In this work, CO2 core flooding experiments were carried out to investigate the effect of CO2 phase on drainage process, especially parameters, such as capillary displacement pressure, relative permeability and displacement efficiency. The results indicated that CO2 phase significantly affected its breakthrough. The breakthrough took place with the least volume of injected liquid CO2 (LCO2) and with the largest volume of injected gas CO2 (gCO2). The capillary displacement pressure was measured based on the jump in the pressure profile and it showed the largest jump in gCO2 drainage. The relative permeability was the largest in LCO2-water displacement and the smallest in gCO2-water displacement. The displacement efficiency can be improved by increasing capillary number when it was smaller than a critical value around 2 × 10-8.