Mattie Garrett (plaintiff) conveyed to Mentor Caldwell “an undivided one sixty-fourth interest in and to all of the [minerals] in and under” a tract of land. The grant was subject to an oil and gas lease (Humphrey Lease) that was in existence at the time the deed was executed, but the grant “cover[ed] and include[d]” one-eighth of the one-eighth royalty that was due to Garrett under the Humphrey Lease. Further, the grant to Caldwell stated that if the Humphrey Lease terminated, Caldwell would own one-eighth of the lease interest and all future mineral rentals because he owned “one-eighth of one-eighth of all oil, gas, and other minerals in and under said lands, together with one-eighth interest in all future rents.” The Humphrey Lease expired under its own terms. Garrett executed another oil and gas lease on the land. The new lease also provided for a one-eighth royalty. Dils Company (Dils) (defendant) acquired Caldwell’s interest under the deed from Garrett. Garrett brought suit for a declaratory judgment on Dils’s interest in the land’s minerals. The trial court held that Dils was entitled to one sixty-fourth of the one-eighth royalty under the new lease. The Texas Court of Civil Appeals reversed, finding that Dils was entitled to one-eighth of the one-eighth royalty. Garrett appealed.