A method for increasing capacity of a natural gas (NG) tank. The method includes selecting a container with a service pressure rating of about 3,000 or 3,600 psi. An NG adsorbent is in the container. The container has a maximum fill capacity. The method further includes cooling the adsorbent by Joule-Thomson cooling during filling of the container with NG from a filling source at greater than 3,600 psi. The container is filled to the maximum fill capacity at a fill rate to prevent a bulk temperature of the adsorbent from rising more than about 5° C. above an ambient temperature. A rate of heat transfer from the tank is less than a rate of heating from compression of the NG and adsorption during the filling. The NG adsorbent adsorbs a higher amount of NG than it would at higher than 5° C. above ambient.