Okla. Stat. tit. 22 § 601a
Whenever in the opinion of the court the trial of a cause is likely to be a protracted one, the court may, immediately after the jury is impaneled and sworn, direct the calling of as many as two additional jurors to be known as "alternate juror". Such alternate jurors shall be drawn from the same source, and in the same manner, and have the same qualifications as regular jurors, and be subject to examination and challenge as such jurors, except that the state shall be allowed one peremptory challenge to each alternate juror, and all parties defendant shall together, or any one party defendant for and on behalf and by the consent of all parties defendant, be allowed one peremptory challenge to each alternate juror.
The alternate jurors shall be sworn (or affirmed) to well and truly try and true deliverance make of all issues finally submitted to them as jurors in said cause, if any such issue shall be so finally submitted to them, and shall be seated near the regular jurors with equal facilities for seeing and hearing the proceedings in the cause, shall attend at all times upon the trial of the cause in company with the regular jurors and shall obey all orders and admonitions of the court; and if the regular jurors are ordered to be kept in the custody of an officer during the trial of the cause, the alternate jurors shall also be kept with the other jurors, and, except as hereinafter provided, shall be discharged upon the final submission of the cause to the jury.
If, before the final submission of the cause to the jury, a regular juror, or two regular jurors, shall be discharged because of illness, or shall die, the court shall order one or both alternate jurors, as circumstances may require, to take their places in the jury box. After an alternate juror is in the jury box, he shall be subject to the same regulations and requirements as other regular jurors.
Okla. Stat. tit. 22, § 601a