34 Tex. Admin. Code § 3.25 - Penalty and Interest

(a) Penalty and interest will not apply to additional value that results from retroactive price increases or retroactive adjustments to value, provided that the additional tax is remitted on or before the 20th day of the second month that follows the month in which such price or value was determined. The taxpayer must notify the comptroller of any tax that is not subject to penalty and interest.

(b) The gas purchaser is responsible for any tax, penalty, and interest that accrues on gas that the purchaser takes whenever the proceeds are not disbursed to the interest owners, unless the producer is solely liable for the tax.