Okla. Stat. tit. 84, § 109

An agreement made by a testator, for the sale or transfer of property disposed of by will previously made, does not revoke such disposal; but the property passes by the will, subject to the same remedies on the testator's agreement, for a specific performance or otherwise, against the devisees or legatees, as might be had against the testator's successors, if the same had passed by succession.