W.R. Blake, Jr. owned the surface and mineral estates in a tract of land. In 1938, Blake, Jr. deeded a portion of the mineral estate to W.R. Blake, Sr. The deed stated that Blake, Jr. granted “an undivided one-sixteenth (1/16) interest in and to all of the oil, gas and other minerals in and under and that may be produced from” the land. The deed also stated that Blake, Sr., the grantee, “does not participate in any rentals or leases.” In 1939, Blake, Jr. deeded the land to D.A. Clark, subject to “one-sixteenth (1/16) of the minerals, non-participating, which has previously been sold.” The land became subject to an oil and gas lease, which reserved a one-eighth royalty for the lessors, Hazel Altman and other heirs of Clark (Clark heirs) (plaintiffs). The Clark heirs sued the heirs of Blake, Sr. (Blake heirs) (defendants). The Clark heirs sought a declaratory judgment defining the interest deeded to Blake, Sr. in the 1938 deed and thus the correct portion of the one-eighth royalty to which the Blake heirs were entitled. The Clark heirs claimed that the 1938 deed conveyed a one-sixteenth ownership interest in the mineral estate, entitling the Blake heirs to one-sixteenth of the one-eighth royalty reserved under the lease. The Blake heirs argued that the 1938 deed conveyed a one-sixteenth royalty interest, entitling them to a one-sixteenth royalty, or one-half of the one-eighth royalty reserved under the lease. The trial court ruled that the 1938 deed conveyed to Blake, Sr. a one-sixteenth, non-participating royalty interest. The court of appeals affirmed. The Clark heirs appealed.