On 17 April 2018, the Colorado communities of Boulder County, San Miguel County, and the City of Boulder filed a lawsuit against Suncor and ExxonMobil, with legal support from EarthRights International, Niskanen Center, and other co-counsel. The communities ask that the oil companies pay their respective share of the costs associated with climate change impacts caused by the use of fossil fuel products. Members of the communities allege that the companies have known about the danger of their products for the climate for 50 years, but have not taken any measures to mitigate risks. The companies deny any wrongdoing.

On 21 June, 2024, Boulder County District Court Judge Robert Gunning defeated motions to dismiss from ExxonMobil Corporation and Suncor subsidiaries' claim that the state court lacked jurisdiction.

On 12 May 2025, the Colorado Supreme Court upheld the lower court’s decision, allowing the case to proceed in state court. In a 5-2 ruling, the justices rejected arguments from ExxonMobil and Suncor that the lawsuit interfered with federal regulation and foreign affairs, affirming that the claims, centred on state law violations and public deception, could be addressed at the state level.

The companies appealed to the Supreme Court asking the case to be stopped. They argue that climate change issues should be heard in federal court. In February 2026, the Supreme Court agreed to hear the case.