Regulations for geological sequestration (GS) of carbon dioxide (CO 2) have been adopted in the state of Washington and proposed by the state of Kansas and the U.S. Environmental Protection Agency (EPA) Underground Injection Control (UIC) Program. These three sets of rules take significantly different approaches to regulating GS of CO 2. This paper compares these rules, focusing on elements where their differences highlight the choices that must be made to create a regulatory framework for GS in the United States. Consensus is emerging in some areas, but there is still substantial disagreement regarding the allowable composition of the CO 2 stream, the size of the area of review, reservoir performance goals, and management of risks other than those to groundwater. Gaps include issuesrelatedtoownershipofsubsurfaceporespace,greenhouse gas accounting, and long-term stewardship. The divergent approaches of these rules raise two overarching questions: (1) Should policy makers create GS regulations by modifying and supplementing UIC rules or through new enabling legislation? (2) What should be the relative roles of state and federal governments in GS regulation? We outline trade-offs between the consistency and coordination that federal involvement could offer and the reality that states need to be heavily involved with implementation of GS regulations. We conclude that federal involvement above and beyond the proposed EPA Class VI rules is needed to create effective GS regulation in the United States.