22 Tex. Admin. Code § 213.12
A witness who is not a party to the proceeding and who is subpoenaed to appear at a deposition or hearing or to produce books, papers, or other objects, shall be entitled to receive reimbursement for expenses incurred in complying with the subpoena as set by the legislature in the APA, Texas Government Code Annotated § 2001.103. In addition, a subpoenaed witness is entitled to thirty dollars ($30) for each day or part of a day that the person is necessarily present, and to mileage reimbursement. The mileage reimbursement rate shall be equal to the maximum fixed mileage allowance specified in the revenue rulings issued by the Internal Revenue Service under the federal income tax regulations as announced by the Texas Comptroller for going to and returning from the place of the hearing or deposition if the place is more than 25 miles from the person's place of residence, and the person uses the person's personally owned or leased motor vehicle for the travel.
22 Tex. Admin. Code § 213.12