Climate mitigation may leave large fossil fuel reserves in the ground. If a State bans extraction to meet its climate obligations, the affected investor may claim that its reserves are stranded assets and that the State must pay. This article asks whether investment treaty law supports that claim. It examines expropriation, legitimate expectations and the police powers doctrine. It reviews arbitral decisions from Tecmed and Saluka to Rockhopper, Eco Oro and Westmoreland. The article argues that the protected asset is the legal right that the State granted and not the reserve. Claims tend to succeed when the State made a specific promise and then acted without due process. Claims tend to fail when the State acted in good faith through a general and non-discriminatory measure.