Tex. Tax Code § 162.369

(a) Except as otherwise provided by this section, a claim for a refund must be filed with the comptroller before the first anniversary of the first day of the calendar month following the purchase, use, or delivery of compressed natural gas or liquefied natural gas, whichever period expires latest.

(b) If the amount of credit that a licensed interstate trucker is entitled to take under Section 162.365(b) exceeds the amount of tax due on that reporting period, the excess credit amount may be claimed on any of three successive quarterly returns following the period in which the credit was established, or the licensed interstate trucker may seek a refund from the comptroller on or before the due date of the third successive quarterly return following the period in which the credit was established. A credit that is not claimed within the period prescribed by this subsection expires.

(c) If the comptroller assesses a dealer for a tax-free sale that is taxable, and the dealer subsequently collects the tax from the purchaser, the purchaser may file a refund claim before the first anniversary of the date the dealer's deficiency assessment becomes final if the purchaser used the fuel in an exempt manner.

(d) A dealer who determines taxes were erroneously reported and remitted or who paid more taxes than were due because of a mistake of fact or law may take a credit on the quarterly tax report on which the error occurred and the tax payment was made to the comptroller. The credit must be taken before the expiration of the applicable period of limitation as provided by Chapter 111.