All persons, firms, corporations or other business organizations engaged in the business of furnishing natural gas in municipalities in this state, to the inhabitants thereof, shall do so through standard meters at meter rates; provided, that this act shall only apply to towns where the population exceeds five hundred (500), and shall not prohibit the sale of gas at a flat rate to federal, state or municipally-owned buildings, institutions or plants; Provided further, that this act shall not abrogate any existing contract, or effect or change the terms or conditions of any franchise granted by any municipal corporation prior to, and in effect April 28th, 1913.
Okla. Stat. tit. 52, § 44