Analysis of well test results and reservoir behavior is presented for a 10,241-t carbon dioxide (CO2) injection test in the Michigan Basin. The test site was located in Otsego County, Michigan, and was part of the Midwest Regional Carbon Sequestration Partnership (MRCSP) program. The injection target was a deep saline rock formation, named the Bass Islands Dolomite, at a depth of 1049–1071 m (3442–3514 ft). Rock core tests on this formation suggested an average permeability of 22 md and porosity of 13% across 22 m (72 ft). Hydraulic monitoring included metering injection at the wellhead and downhole pressure and temperature logging in the injection well and a nearby deep monitoring well. Pressure response curves were analyzed for a step-rate injection and shut-in recovery tests. Downhole pressure in the injection well was approximately 13,800–13,930 kPa at injection rates of 400–600 t CO2 per day. Step-rate injection testing suggested that injection rates of several hundred thousand metric tons CO2 per year may be sustainable in a single well. Injection test pressure falloff analysis showed that the overall reservoir permeability may be more than twice as high as indicated from rock core tests. This successful test provides extremely valuable field information on all aspects of the CO2 storage feasibility for both the test region and the broader deployment of the technology.