Causes and effects of global warming are a highly debated topic. Nonetheless injection and storage of CO2 (CO2 sequestration) in the subsurface has been becoming an accepted practice to reduce the amount of CO2 from atmosphere, which is a primary contributor to the global warming. Monitoring of CO2 movement with time is essential to ensure that sequestration is not hazardous. We propose a method to assess CO2 saturation using pressure dependent differential effective medium theory (DEM). According to the conventional DEM theory, cavities are isolated with respect to fluid flow, but pressure-dependent DEM theory accounts for wave induced fluid flow between cavities. Our study area is the Cretaceous lower Tuscaloosa formation at Cranfield in Mississippi, USA, which is one of the active enhanced oil recovery (EOR), and CO2 capture and storage (CCS) fields. One injection well (F1) and two observation wells (F2 and F3) are present closely (within 112 meters) in our area of study within this region. Since the three wells are closely situated, we have focused on the injection well F1 and the furthest observation well F3 to monitor CO2 movement. Time-lapse (pre- and post injection) log, core and surface seismic data are used for quantitative assessment of CO2 saturation using our rock physics model. We estimate an average CO2 saturation in F1 to be 55-60% and that in F3 to be 50-55% in an injection zone of thickness ~25 m at a depth ~3 kilometer after approximately nine months of injection.