The petroleum system is classically defined in Exploration applications as a unifying concept that integrates all relevant aspects of petroleum geology building on four key elements: reservoir, seal, charge and trap. This can be adapted into a holistic framework for CO2 sequestration site identification. Of the four key petroleum system elements, reservoir and trap can be treated in a similar way for CO2 sites in terms of mapping, characterization, volumetrics and so on. On the other hand, seal and charge have important differences and consequences in the CO2 sequestration realm. The dynamics of CO2 in the subsurface also have to be fully integrated. Key features include phase changes from gas to supercritical fluid, and long term dissolution into reservoir water legs. Because CO2 solutions are denser than the initial solvent, they sink into reservoirs, inverting the trapping concept such that negative buoyancy traps should be included. Basin hydrostratigraphy becomes important as does any fluid movement in reservoirs driven by hydraulic head gradients, which introduce tilted contacts to which CO2 solutions are particularly sensitive. Site characterization programs can account for all of these factors in a systems framework.