In 2012, the U.S. Geological Survey (USGS) completed an assessment of the technically accessible storage resources (TA_SR) for carbon dioxide (CO₂) in geologic formations underlying the onshore and State waters area of the United States. The formations assessed are at least 3,000 feet (914 meters) below the ground surface. The TA_SR is an estimate of the CO₂ storage resource that may be available for CO₂ injection and storage that is based on present-day geologic and hydrologic knowledge of the subsurface and current engineering practices. Individual storage assessment units (SAUs) for 36 basins were defined on the basis of geologic and hydrologic characteristics outlined in the assessment methodology of Brennan and others (2010, USGS Open-File Report 2010–1127) and the subsequent methodology modification and implementation documentation of Blondes, Brennan, and others (2013, USGS Open-File Report 2013–1055). The mean national TA_SR is approximately 3,000 metric gigatons (Gt). The estimate of the TA_SR includes buoyant trapping storage resources (B_SR), where CO₂ can be trapped in structural or stratigraphic closures, and residual trapping storage resources, where CO₂ can be held in place by capillary pore pressures in areas outside of buoyant traps. The mean total national B_SR is 44 Gt. The residual storage resource consists of three injectivity classes based on reservoir permeability: residual trapping class 1 storage resource (R1_SR) represents storage in rocks with permeability greater than 1 darcy (D); residual trapping class 2 storage resource (R2_SR) represents storage in rocks with moderate permeability, defined as permeability between 1 millidarcy (mD) and 1 D; and residual trapping class 3 storage resource (R3_SR) represents storage in rocks with low permeability, defined as permeability less than 1 mD. The mean national storage resources for rocks in residual trapping classes 1, 2, and 3 are 140 Gt, 2,700 Gt, and 130 Gt, respectively. The known recovery replacement storage resource (KRR_SR) is a conservative estimate that represents only the amount of CO₂ at subsurface conditions that could replace the volume of known hydrocarbon production. The mean national KRR_SR, determined from production volumes rather than the geologic model of buoyant and residual traps that make up TA_SR, is 13 Gt. The estimated storage resources are dominated by residual trapping class 2, which accounts for 89 percent of the total resources. The Coastal Plains Region of the United States contains the largest storage resource of any region. Within the Coastal Plains Region, the resources from the U.S. Gulf Coast area represent 59 percent of the national CO₂ storage capacity.