Dynamic seismic inversion builds time-lapse (4D) data into the static inversion to take into account multiple surveys. RSS has extended its AVO and inverse modeling techniques to solve for acoustic and elastic rock properties for 4D seismic data. Base-to-monitor survey matching, sequential impedance inversion, and 4D ISIS simultaneous inversion are performed to generate time-lapse impedance, compressional velocity, shear velocity, and density cubes. ISIS simultaneous inversion enhances the accuracy of time-lapse seismic analysis. Full-stack, partial-stack, and prestack seismic data for any number of vintages can be inverted simultaneously.