The estate of H. H. Coffield (estate) (defendant) sold 4,000 acres of real estate to Thompson (plaintiff). Prior to the sale, the estate executed several coal leases in favor of a mining company, which were confirmed by the probate court but not recorded with the county clerk. The deed to Thompson reserved a one-half interest in the mineral royalties to the estate. The deed also stated that mineral interests covered by a valid, recorded lease would not vest in Thompson until the lease expired and that interests covered by a top lease that were either validly recorded or confirmed by the probate court would not vest in Thompson until the leases expired. Thompson sued the estate for $40,000 in royalties due under the estate’s leases, arguing that, because the leases were not recorded, one-half of the mineral interests were transferred to Thompson at the time of the sale, rather than at the expiration of the leases. The estate counterclaimed for reformation of the contract, arguing that Thompson was aware of the leases at the time of the sale and that both parties understood that the estate would retain all of the royalty interests under the leases until they expired. The trial court refused to admit any evidence extrinsic to the deed and entered judgment in favor of Thompson. The estate appealed, and the court of appeals affirmed. The Oklahoma supreme court granted certiorari.