Okla. Stat. tit. 28 § 91
In civil cases in which the state is not a party, if the State Fire Marshal or an employee of the Office of State Fire Marshal is subpoenaed as a witness to testify on any matter pertaining to a fire investigation conducted by the Office of State Fire Marshal, the party causing the subpoena to be issued shall pay an expert witness fee to be set by the State Fire Marshal. Said fee shall be paid to the court clerk before the witness is required to testify. The court clerk shall remit the fee to the State Treasurer to be deposited to the General Revenue Fund of the state.
Notice of receipt of the required fee shall be transmitted by the court clerk to the State Fire Marshal or employee who has been subpoenaed. If the expert witness fee is not received before the witness is required to testify, the witness shall not be compelled to obey the subpoena.
If the expert witness fee is paid and, for any reason, the witness fails to obey the subpoena, said fee shall be returned to the party causing the subpoena to be issued.
Okla. Stat. tit. 28, § 91