Sun Oil Co. v. Wortman, 486 U.S. 717 (1988), was a conflict of laws case decided by the United States Supreme Court.

The facts were similar to the case of Phillips Petroleum Co. v. Shutts, also being a class action lawsuit in Kansas for overdue interest payments, with plaintiffs from all fifty U.S. states.

The majority opinion, by Justice Scalia, held that there can never be a violation of Fourteenth Amendment Due Process or Full Faith and Credit if a state interprets as procedural something that has been deemed procedural by states in general for hundreds of years.

In this case, there was no problem because Kansas is not limiting substantive rights granted by other states by allowing plaintiffs to bring these claims for a longer time, the presumption being that other states enact limitations designed to unburden their own courts.

A dissent by Justice O'Connor, joined by Chief Justice Rehnquist, asserted that the Kansas Supreme Court violated the Full Faith and Credit Clause by ignoring statutory interest rates imposed by three other states.