The method of transferring compressed gas at from a first tank to a second tank without decompressing the compressed gas and then re-pressuring the compressed gas comprising filling the second tank with a fluid, connecting a first fluid connection on the first tank to a second fluid connection on the second tank with a first line with one or more first valves, connecting a first gas connection on the first tank to a second gas connection on the second tank with a second line with one or more second valves, opening the first valves and the second valves to allow the compressed gas to pressurize the fluid, and pumping the fluid in the second tank into the first tank, thereby causing the compressed gas in the first tank to be displaced into the second tank.