A gas storage container, such as a gas cylinder, is filled with a gas mixture comprising a first gas and a second gas under pressure by feeding a liquid/solid mixture comprising liquefied first gas and solidified second gas into the gas storage container； closing the gas storage container to the passage of gas into or out from the container； and allowing said liquefied first gas and said solidified second gas to become gaseous within said closed gas storage container. Such a process is easier and more energy efficient as compared to direct compression processes, and is safer and results in less wastage as compared to direct liquid injection processes.
