The success of geologic carbon dioxide (CO2) sequestration as a large-scale carbon management strategy is critically dependent on the ability of the geologic sinks and trapping mechanisms to confine the injected CO2 for hundreds to thousands of years. Leakage of CO2 from geologic sinks could result in significant release of the CO2 back to the atmosphere, potentially reducing, if not negating altogether, the benefits of geologic CO2 sequestration. For example, a leakage rate of 1% per year from 1 billion tons of geologically stored CO2 (10 million tons) would exceed the current annual CO2 emissions from all the power plants in North Dakota (4 million tons). Further, leakage could have negative ecological effects and present the potential for health problems other than global warming.