This invention relates to a novel method and system for dispensing CO2 vapor without over pressurization. The system includes one or more liquid containers and one or more vapor containers. The system is designed to operate in a specific manner whereby a restricted amount of CO2 liquid is permitted into the vapor container through a restrictive pathway that is created and maintained by a shuttle valve during the filling operation so that equalization of container pressures is achieved, thereby allowing shuttle valve to reseat when filling has stopped. During use, a pressure differential device is designed to specifically isolate the vapor container from the liquid container so as to preferentially deplete liquid CO2 from the vapor container and avoid over pressurization of the system until the vapor container. The system is operated so that at least 50% of the CO2 product is dispensed from the vapor container. The system also includes novel control methodology for performing pre-fill integrity checks to ensure safety of subsequent dispensing of CO2 liquid from a source vessel to the onsite CO2 containers.