Tex. Tax Code § 162.128

(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, delivery, or export, or loss by fire, theft, or accident of gasoline, whichever period expires latest.

(b) If the amount of credit that an interstate trucker is entitled to take under Section 162.125 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 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 supplier or permissive supplier for a tax-free sale that is taxable, and the supplier or permissive supplier subsequently collects the tax from the purchaser, the purchaser may file a refund claim before the first anniversary of the date the supplier's or permissive supplier's deficiency assessment becomes final if the purchaser used the gasoline in an exempt manner.

(d) A supplier, permissive supplier, distributor, importer, exporter, or blender that determines taxes were erroneously reported and remitted or that paid more taxes than were due this state because of a mistake of fact or law may take a credit on the monthly tax report on which the error has occurred and tax payment made to the comptroller. The credit must be taken before the expiration of the applicable period of limitation as provided by Chapter 111.