A subterranean tank can consist of at least a casing string that has a containment section disposed between first and second end regions. The containment section may have a first width while each of the first and second end regions have a second width. The first width can be greater than the second width of the respective first or second end regions. The entire casing string may be sealed to maintain a gas at 5,000 psi or more until a gas delivery assembly attached to the first end region releases gas stored in the casing string.