Okla. Stat. tit. 68 § 804
In case the tax levied upon the value of the property of the estate in Oklahoma and transfers by Section 801 et seq. of this title is less than the credit allowed by the federal government on estate tax imposed upon the value of the property of the estate in Oklahoma, for state estate and inheritance taxes imposed upon the value of the property of the estate in Oklahoma, pursuant to 26 U.S.C. Section 2011, then, in that event, there shall be levied an additional tax which shall be imposed upon the value of the property of the estate in Oklahoma, as of the date of the determination of the Federal Estate Tax, equal to the difference between such credit and the Oklahoma Estate Tax levied upon the value of the property of the estate in Oklahoma and transfers by this Article. Such credit allowed by the federal government shall be the percentage of such credit which is the percentage which the value of the property of the estate in Oklahoma bears to the total value of the estate of the decedent. Such additional tax to absorb the credit shall be determined, assessed, collected and paid pursuant to the provisions of Section 801 et seq. of this title.
Okla. Stat. tit. 68, § 804