AbstractLeakage of brine or carbon dioxide (CO2) from geologic CO2 storage reservoirs will trigger numerous costs. We present the Leakage Impact Valuation (LIV) method, a systematic and thorough scenario-based approach to identify these costs, their drivers, and who incurs them across four potential leakage outcomes: 1) Leakage only; 2) leakage that interferes with a subsurface activity; 3) leakage that affects groundwater; and 4) leakage that reaches the surface.The LIV method is flexible and can be used to investigate a wide range of scenarios. The financial consequences of leakage estimated by the LIV method will be specific to the case study, because the consequences of leakage will vary across case studies due to differences geologic, institutional, and regulatory settings