Okla. Stat. tit. 30 § 2-106
A minor's parent who is competent to transact his or her own business and not otherwise unsuitable or disqualified by law to serve as the guardian of said minor, shall be entitled to the guardianship of the minor until the minor has attained the age of fourteen (14) years. The parent petitioning the court for appointment as guardian of the minor must have the endorsement or nomination of the other parent, if the natural parents of the minor are married and living together. In cases where both parents are separately seeking appointment as guardian of the minor, the court may, upon full investigation, appoint the parent who in the judgment of the court is the most competent to look after the interest of said minor.
Okla. Stat. tit. 30, § 2-106