Whenever the full production from any common source or field of supply of natural gas in this state is in excess of the market demands, then any common purchaser of such natural gas as herein defined receiving production or output from such source or field shall take therefrom only such proportion of the available supply as may be marketed and utilized without waste, as the natural flow of the well or wells owned or controlled by such common purchaser bears to the total natural flow or production of such common source or field, having due regard to the acreage drained by each well, so as to prevent any common purchaser from securing an unfair proportion therefrom; and it shall be the duty of the commission and it is hereby empowered to regulate and enforce the above provision, provided that the commission may by proper order permit the taking of a greater proportion by any common purchaser whenever or wherever it shall determine a taking of such greater proportion reasonable and equitable or conducive to public convenience or necessity.