Tex. Natural Resources Code § 87.171: GAS CONTAINING LOW HYDROCARBON CONTENT.

Any natural gas, including casinghead gas, produced from any gas well or oil well in this state, containing less than one and one-half gallons of propane and heavier hydrocarbons per 1,000 cubic feet, as determined by fractional analysis made of the gas, may be used for the manufacture of carbon black in a plant producing an average recovery of at least one and one-half pounds of carbon black for each 1,000 cubic feet of gas consumed.

Acts 1977, 65th Leg., p. 2545, ch. 871, art. I, Sec. 1, eff. Sept. 1, 1977.