A binational effort between the United States and Canada is under way to characterize the lowermost saline system in the Williston and Alberta Basins of the northern Great Plains–Prairie region of North America in the United States and Canada. This 3-year project is being conducted with the goal of determining the potential for geologic storage of CO2 in rock formations of the 1.34-million-km2 Cambro-Ordovician Saline System (COSS). To our knowledge, no other studies have attempted to characterize the storage potential of large, deep saline systems that span the U.S.–Canada international border. This multiprovince/multistate, multiorganizational, and multidisciplinary project is led on the U.S. side by the Energy & Environmental Research Center (EERC) through the Plains CO2 Reduction (PCOR) Partnership and on the Canadian side by Alberta Innovates Technology Futures (AITF). The project objectives are to characterize this basal system in the northern Great Plains–Prairie region of North America and to evaluate its potential for, and effects of, CO2 storage in this system. At the base of the sedimentary succession in the Williston and Alberta Basins of the northern Great Plains–Prairie region of North America is a saline system composed of variable lithology which includes a variety of clastic and carbonate facies deposited across a range of environments. This system lies directly on top of igneous and metamorphic basement rocks and is largely contained beneath sealing formations that include shales and tight carbonates. These Middle Cambrian- to Lower Silurian-aged rocks extend from west-central Alberta into Saskatchewan, southwestern Manitoba, and then south into Montana, North Dakota, and South Dakota and form an extensive saline system generally devoid of hydrocarbon resources. In the area underlain by the COSS, there are 43 large CO2 sources that each emit more than 0.75 Mt CO2/year. Assuming that all of these emissions from each of these sources will be stored in the COSS, the main questions to be addressed by this study are 1) what is the storage resource of the system?, 2) how many years of CO2 emissions will it be capable of storing?, and 3) what will the fate and effects of the stored CO2 be? The project started on October 1, 2010, and is structured in three 1-year phases. Phase I focused on delineating and characterizing separately the Canadian and U.S. portions of the COSS. These were subsequently brought together into a single model during Phase II. The completed 2-D model incorporates the geologic data collected in the baseline characterization effort and distributes the various rock properties throughout the study region through geostatistical methods. Data on depth, thickness, and porosity were distilled v to produce components needed to compute the CO2 storage resource of this saline system following the Esaline formula detailed by the U.S. Department of Energy (DOE) methodology. A significant part of the effort was to match the work done on the U.S. side of the study region with the data sets generated by AITF for the Canadian side. All necessary gridded interpolations on the U.S. side were combined with the Canadian grids by a diffusive aggregation method near the U.S.–Canadian border to form a seamless CO2 storage volume for the entire COSS international study region. This aggregation method involved feathering the Canadian data near the border and joining it to the data on the U.S. side, thus allowing the geostatistical processing functions to interpolate across the border and avoid the development of edge effect at the border. Once the calculation on the U.S. side was completed, it was clipped out and joined to the existing Canadian portion to form a seamless map. This novel approach worked well for joining the two data sets, and the resulting 2-D model indicated a storage resource of 113 Gt. This work also provides the groundwork for the development of a massive 3-D geologic model encompassing the entire study area. In addition to the leading organizations of the EERC and AITF, other partners in the project are DOE, Lawrence Berkeley National Laboratory, and Princeton University in the United States and Saskatchewan Industry and Resources, Manitoba Water Stewardship, Manitoba Innovation – Energy and Mines, CanmetENERGY, Natural Resources Canada, TOTAL E&P Ltd., and the University of Regina Petroleum Technology Research Centre in Canada.