The U.S. Supreme Court case American Oil Co. v. Neill et al., 1964, revolved around the issue of whether a state could impose its own tax on gasoline that was purchased in another state but used within its borders. The State of Idaho had imposed such a use tax on an interstate motor carrier company (Neill), which bought fuel in Oregon where it was cheaper due to lower taxes and then used it for operations in Idaho. The American Oil Company, who sold the gas to Neill, challenged this law arguing that it violated the Commerce Clause of the Constitution by placing an undue burden on interstate commerce. However, the Supreme Court upheld Idaho's right to levy such a tax ruling that as long as there is no discrimination against out-of-state businesses or products and if revenue generated from taxation is fairly related to services provided by the state, then these laws do not violate constitutional principles governing interstate commerce.

In the dissenting opinion for American Oil Co. v. Neill et al., the justice argued that Idaho's law, which prohibited oil companies from leasing service stations to independent operators and then supplying them with gasoline at a lower price than other dealers, was unconstitutional. The justice believed that this law violated the Commerce Clause of the U.S Constitution by directly regulating interstate commerce and discriminating against it in favor of local business interests. They also contended that there was no substantial evidence provided to support Idaho's claim that such practices were harmful or unfair to competition within their state borders; therefore, they saw no legitimate public interest being served by this regulation. Furthermore, they pointed out inconsistencies in how similar laws had been treated across different states as an issue needing further clarification from the court.