This working paper outlines a recommended methodology for estimating and reporting the potential emissions from fossil fuel reserves held by coal, oil, and gas companies. The overall goal is the availability of transparent, credible, and consistent data on potential emissions that help illuminate companies’ effects on the carbon budget and inform investment strategies and decisions to use reserves. While the methodology can be directly used by fossil fuel companies to disclose potential emissions data, other groups, such as civil society organizations, investors, and stock market listing authorities, can use the methodology indirectly to press for disclosure.