Supreme Court Hears Boulder Climate Case Testing State-Law Claims Against Oil Companies

The Supreme Court heard arguments this week in a closely watched climate-liability case that could shape whether Boulder, Colorado, and other local governments may use state law to seek payments from oil companies for climate-related harms.

At issue in Suncor Energy (U.S.A.) Inc., et al. v. County Commissioners of Boulder County, et al., No. 25-170, are two questions: whether the justices have the statutory and constitutional authority to hear the dispute now, and whether federal law bars state-law claims seeking relief for injuries allegedly caused by interstate and international greenhouse-gas emissions. The court has not issued a decision.

The case was the first argument of the court’s October 2026 term. Arguments began at 10:06 a.m. on Oct. 5. Petitioners Suncor Energy (U.S.A.) Inc. and ExxonMobil are challenging Boulder County and the city of Boulder, which sued under state law. Kannon K. Shanmugam argued for the companies, Kevin K. Russell argued for Boulder, and Sarah M. Harris argued for the United States as a friend of the court in support of the companies.

The Justice Department backed Suncor and ExxonMobil, arguing that federal law and federal interests in a uniform national policy weigh against allowing state tort law to govern claims over global greenhouse-gas emissions. In its brief, the government framed one threshold issue as “Whether this Court has statutory and Article III jurisdiction to hear this case.” At the hearing, Shanmugam told the justices, “This case involves an unprecedented effort to use state law to regulate global conduct.”

Boulder’s underlying lawsuit dates to 2018. The county and city seek monetary damages tied to local climate-related harms, including the costs of adapting to and mitigating those harms. The suit does not seek an injunction directly controlling emissions.

The case reached the nation’s highest court after the Colorado Supreme Court ruled on May 12, 2025, that Boulder’s state-law claims could proceed and were not preempted by federal law. That ruling did not decide whether Boulder’s claims were valid on the merits; it allowed the case to continue. The U.S. Supreme Court granted review on Feb. 23, 2026, and added the jurisdiction question when it took the case.

The dispute is being closely watched because dozens of similar suits filed by states, cities, counties and tribes are pending around the country. Those cases generally seek to hold major fossil fuel companies financially responsible for local costs linked to climate change, using state-law theories rather than asking courts to set nationwide emissions rules.

That distinction helps explain why the Boulder case matters. This is not a trial over whether climate change exists. The legal fight is over who gets to regulate or assign liability for climate-related harms: state courts applying state tort law, or the federal government through federal law. The case also sits against the backdrop of the Supreme Court’s 2011 decision in American Electric Power Co. v. Connecticut, which held that the Clean Air Act displaced federal common-law nuisance claims aimed at curbing carbon-dioxide emissions. The Boulder dispute presents a related but different question: whether state-law damages claims may still move forward.

A ruling for the companies could sharply narrow the path for state and local climate-damages suits that target global emissions through state law. A ruling for Boulder could allow more of those cases to continue in state courts, even if it does not resolve the underlying claims themselves.