Tex. Natural Resources Code § 87.132

(a) Gas from any gas well completed on or before September 5, 1947, within a common reservoir producing both sweet and sour gas from which the gas was not sold off the leased premises to an interstate pipeline company during the year immediately preceding September 5, 1947, or gas from any gas well completed after September 5, 1947, within a common reservoir producing both sweet and sour gas, may be used for the manufacture of carbon black without the prior extraction of its natural gasoline content if:

(1) it is used in a plant producing an average recovery of not less than one and one-half pounds of carbon black for each 1,000 cubic feet of gas; and

(2) the royalty rate and market price paid for the gas at the wellhead at least equals the royalty rate and market price paid at the wellhead in the immediate area for gas used for light and fuel purposes.

(b) In arriving at the market price of sour gas, a reduction of not more than one-half cent per 1,000 cubic feet shall be allowed for purifying the gas to render it suitable for light and fuel purposes.

(c) If the gas is used by a producer, any royalty rate paid shall be paid on the same basis.