Carbon capture from stationary sources and geologic storage of carbon dioxide (CO₂) is an important option to include in strategies to mitigate greenhouse gas emissions. However, the potential costs of commercial-scale CO₂ storage are not well constrained, stemming from the inherent uncertainty in storage resource estimates coupled with a lack of detailed estimates of the infrastructure needed to access those resources. Storage resource estimates are highly dependent on storage efficiency values or storage coefficients, which are calculated based on ranges of uncertain geological and physical reservoir parameters. If dynamic factors (such as variability in storage efficiencies, pressure interference, and acceptable injection rates over time), reservoir pressure limitations, boundaries on migration of CO₂, consideration of closed or semi-closed saline reservoir systems, and other possible constraints on the technically accessible CO₂ storage resource (TASR) are accounted for, it is likely that only a fraction of the TASR could be available without incurring significant additional costs. Although storage resource estimates typically assume that any issues with pressure buildup due to CO₂ injection will be mitigated by reservoir pressure management, estimates of the costs of CO₂ storage generally do not include the costs of active pressure management. Production of saline waters (brines) could be essential to increasing the dynamic storage capacity of most reservoirs, but including the costs of this critical method of reservoir pressure management could increase current estimates of the costs of CO₂ storage by two times, or more. Even without considering the implications for reservoir pressure management, geologic uncertainty can significantly impact CO₂ storage capacities and costs, and contribute to uncertainty in carbon capture and storage (CCS) systems. Given the current state of available information and the scarcity of (data from) long-term commercial-scale CO₂ storage projects, decision makers may experience considerable difficulty in ascertaining the realistic potential, the likely costs, and the most beneficial pattern of deployment of CCS as an option to reduce CO₂ concentrations in the atmosphere.