John L. McMahon, Junior v. John J. Christmann

Summary

The Texas Supreme Court held that the proportionate reduction clause in the oil, gas and mineral lease applies only to the ordinary royalty and not to the overriding royalty expressly reserved "without reduction," resulting in a total royalty of 5/96ths of production. The Court declined to apply the Duhig estoppel rule to mineral leases and reversed the lower courts, remanding for trial on the respondents' cross‑action for reformation. Justice Garwood dissented, arguing the Duhig rule should apply, and Justice Smith concurred in part, urging reversal of the judgment.