As used in this article, the term:

(1) "Gas" means natural gas or manufactured gas, or a combination of both.

(2) "Gas utility" means any individual, firm, corporation, organization, or other entity holding a certificate of public convenience and necessity issued by the commission authorizing the transportation, distribution, or sale of gas.

(3) "Underground reservoir" means any subsurface sand, strata, formation, aquifer, cavern, or void, whether natural or artificially created, which is suitable for the injection and storage of gas therein and for the withdrawal of gas therefrom.