Substantial risks of environmental damage from oil spills are associated with ocean transport of oil by tanker. These risks have been magnified with the advent of the behemoths known as "supertankers," which can carry up to twelve times as much oil as ordinary tankers. Collision or grounding of tankers is more likely to occur close to shore, where tanker navigation can be especially difficult. Puget Sound, a unique (and narrow) coastal estuary in Washington, poses just such navigation difficulties for the tankers that service refineries located adjacent to the Sound.

Recognizing these risks, the state of Washington in 1975 enacted the Tanker Law,¹ which prohibits the passage of supertankers and regulatesthe navigation of other oil tankers in Puget Sound. Atlantic Richfield, an oil company and owner of one of the refineries, and Seatrain Lines, a shipbuilding and ship-operating company, filed suit to enjoin the statute's effect, claiming that federal law preempts state regulation of oil tankers and that the state statute conflicted with the exclusive federal power in the areas of commerce and foreign affairs. On September 23, 1976, in Atlantic Richfield Company v. Evans,² a three-judge federal district court declared Washington's Tanker Law void as preempted by federal law, primarily the Ports and Waterways Safety Act (PWSA).³ The court later issued a permanent injunction against enforcement of the Tanker Law on November 12, but stayed its effect until December 15. Washington appealed to the Supreme Court and Justice Rehnquist, as Circuit Justice, continued the stay pending a hearing on the state's application before the entire Court.⁴