power under their tribal sovereignty to impose taxes on the reservation. The court also held that the tax did not violate the Commerce Clause nor place an undue burden on the oil companies. Opinion of the Court Initial arguments The oil companies immediately appealed and the United States Supreme Court granted certiorari to hear the case. This appeal came shortly after the Supreme Court had decided Oliphant v. Suquamish Indian Tribe, , which had stated that an Indian tribe did not have the authority to try a non-Indian for a crime committed on the reservation. The Oliphant case was a major blow against tribal sovereignty, and was a case used by the oil companies in their briefs. The oil companies argued that Oliphant, currently limited to criminal cases, should be expanded to civil matters as well. The attorneys for the tribe argued that this case was no different than Washington v. Confederated Tribes of Colville Indian Reservation, , which stated that tribes had the authority to impose a cigarette tax on both tribal members and non-Indians alike. Amici briefs were filed by Montana, North Dakota, Utah, Wyoming, New Mexico, Washington (state), the Mountain States Legal Foundation, the Salt River Project Agricultural Improvement and Power District, Shell Oil, and Westmoreland Resources in support of the oil companies. The Council of Energy Resource Tribes and the Navajo Nation filed briefs supporting the tribe. Arguing for Mellion and Bayless was Jason W. Kellahin, for Amoco and Marathon Oil was John R. Cooney (originally a separate case, but which was consolidated with this case), for the tribe was Robert J. Nordhaus, and on behalf of the tribe for the Solicitor General was Louis F. Claiborne. Kellahin argued that tribal sovereignty only extended to members of the tribe, citing both Oliphant and Montana v. United States, , both cases involving the jurisdiction of a tribal court over non-Indians. Kellahin stated that those cases that allowed a tribe to tax non-Indians were not due to tribal sovereignty, but were connected with the authority of the tribe to regulate who could enter the reservation, in the same manner as a landlord controlled their property. Cooney argued that the tax was a violation of the Commerce Clause, in that Congress divested the tribes of that authority when they enacted granting the states the right to impose a severance tax on reservation lands. Nordhaus, in arguing for the tribe,