Susan Davis Van Dyke v. the Navigator Group, 668 S.W.3d 353

1924 deed from George and Frances Mulkey reserved “one-half of one-eighth of all minerals and mineral rights.”
For ~90 years subsequent transactions (conveyances, leases, division orders, stipulations, etc.) uniformly treated each side (Mulkey and White successors) as owning an undivided one-half mineral interest.
In 1946 a Mulkey family letter referenced a contract giving the Mulkeys one-half the minerals; no contemporaneous deed/contract has been found.
In 2013 White successors sued (trespass to try title) after royalties were paid 50/50; trial court granted White partial summary judgment holding the reservation unambiguously conveyed a 1/16 interest; court of appeals affirmed.
The Supreme Court of Texas reversed: (1) as a matter of deed construction, the double-fraction phrase presumes 1/8 functioned as a term of art referring to the whole mineral estate, so “one-half of one-eighth” reserved one-half; and (2) alternatively, the presumed-grant doctrine independently vests the Mulkeys with one-half on the undisputed long history of open, acquiesced claims.
Case remanded to the trial court for further proceedings consistent with that ruling.

Issue	Mulkey's Argument	White's Argument	Held
Proper construction of reservation phrase “one-half of one-eighth”	In 1924 usage, 1/8 in double fractions was a term of art meaning the whole mineral estate, so the phrase reserved one-half the estate	Phrase is literal arithmetic; one-half × one-eighth = 1/16 reserved to Mulkeys	Deed construed for Mulkeys: presumption that 1/8 was term-of-art in double fractions not rebutted by the instrument; reservation equals one-half of the mineral estate
Application of presumed-grant doctrine to vest additional title	Even if deed initially reserved only 1/16, decades of open, consistent transactions and non-claim by Whites satisfy presumed-grant elements and vest the Mulkeys with the other 7/16	Doctrine inapplicable; court of appeals required a title “gap” and found none	Court held presumed-grant doctrine satisfied (long open adverse claim, nonclaim and acquiescence); even if unnecessary, it independently confirms Mulkeys’ one-half ownership

Hysaw v. Dawkins, 483 S.W.3d 1 (Tex. 2016) (analyzed the “double-fraction dilemma,” recognized 1/8 as a historical term-of-art and set out contextual presumption with possible rebuttal)
Garrett v. Dils Co., 299 S.W.2d 904 (Tex. 1957) (judicial notice of historical double-fraction usage in mineral instruments)
URI, Inc. v. Kleberg County, 543 S.W.3d 755 (Tex. 2018) (textual interpretation defaults to a term’s ordinary meaning at the time of drafting)
New Prime Inc. v. Oliveira, 139 S. Ct. 532 (2019) (statutory phrase meaning is determined by public meaning at enactment date)
Concord Oil Co. v. Pennzoil Expl. & Prod. Co., 966 S.W.2d 451 (Tex. 1998) (discussed estate-misconception: lessor retained more than a mere 1/8 royalty interest)