Here is the opinion in Neptune Leasing Inc. v. Mountain States Petroleum Corp. and Nacogdoches Oil and Gas Inc. The court’s syllabus:

The Supreme Court issues its opinion in this appeal of the Shiprock Court’s dismissal of a repossession action on the basis of a lack of personal jurisdiction over Mountain States. The Court reverses and remands for further proceedings. The action concerns the sale and re-sale of a helium plant and its assets located on a Navajo Nation business site leasehold performed without involvement or consent of the Navajo Nation and without even a written business site lease. Finding that the Shiprock Court erred in providing conclusory findings as to jurisdiction, the Court found jurisdiction after engaging in a full jurisdictional discussion involving inherent sovereignty, Navajo statutes, and federal common law tests. The parties had additionally challenged subject matter jurisdiction on the basis of a private agreement between the purported buyer and seller which selected Texas as their litigation forum; however the Court stated that no private contractual clause may avoid Navajo Nation jurisdiction over transactions on Navajo Nation land involving assets in which the Navajo Nation may have an interest. Additionally, the Court repeated that there is no such things as an equitable business site lease.