Editor's Summary: To address potential global climate change caused by rising concentrations of atmospheric carbon dioxide (CO2), many are advocating CO capture and sequestration, which involves the injection of CO into geologic formations. But because of the large volumes of CO that would need to be injected annually, the long storage time frames required for geological sequestration, and the monitoring and verification needs for injected CO2, this technology presents a novel set of demands on the current legal regime for subsurface property rights. This Article focuses on the legal precedents for underground injection and examines the existing case law framework that could influence legal interpretations of future geological sequestration projects. The authors argue that clarification of property rights as they relate to geological sequestration is important from both regulatory and liability perspectives, as each can have significant impacts on the future cost, public acceptability, and feasibility of geological sequestration projects.