The goal of this project is to improve current methods of rock physics and time-lapse seismic reflection modeling for CO2 sequestration and miscible CO2 floods in oil and gas reservoirs, and to develop new strategies to invert such data to estimate changes in pressure, oil saturation, water saturation, and CO2 saturation over time. The project consists of three phases. In Phase I new ways to calculate fluid properties of oil-water-CO2 mixtures under varying reservoir conditions are being investigated. A thorough literature search has revealed two major approaches for accomplishing this: using either an equation-of-state (EOS) formulation or molecular dynamics simulations. These two approaches are being compared for robustness and accuracy. A preliminary EOS formulation has been developed that is capable of calculating bulk fluid properties from multiple liquid and gas phases for supercritical CO2 mixtures. In Phase II this EOS is being used to perform 1-D time-lapse seismic modeling by calculating changes in well-log velocities and densities under varying CO2 saturations and pressures. In addition, progress has been made in building a 3-D seismic modeling tool that can be used to predict time-lapse seismic anomalies in 3-D field data. In Phase III, a method is being developed to invert time-lapse seismic anomalies to yield maps of CO2 saturation and pressure changes over time. The first step of this method which generates seismic attributes as a function of CO2 saturation and pressure changes, including changes in both miscible and free CO2 levels has been completed.