The U.S. Department of Energy (DOE), through its National Energy Technology Laboratory (NETL), established a national program to evaluate the feasibility of separating carbon dioxide (CO2) from industrial sources and pumping it underground for long-term storage or disposal. This program was established in response to concerns that CO2 emissions from fossil-fuel combustion, and from other industrial processes such as cement production from limestone, are increasing atmospheric CO2 concentration and solar-energy absorption, thereby causing global warming. Carbon dioxide removal from industrial sources and storage in geologic reservoirs is known as “geologic sequestration.” A major aspect of the DOE program is to evaluate subsurface geology to determine the potential of underground rock formations for long-term CO2 sequestration. WESTCARB (West Coast Regional Carbon Sequestration Partnership) is a consortium of seven western U.S. States and one Canadian Province that is one of seven regional North American partnerships established to evaluate technical aspects of high-volume CO2 capture and sequestration. Collaborative WESTCARB research programs have included more than 90 public agencies, private companies, and non-profit organizations. The Arizona Geological Survey began work in 2010 on WESTCARB Phase III – Arizona Geological Characterization. This report represents an initial WESTCARB assessment of CO2 storage potential in Arizona’s Cenozoic basins, and is part of Task 2 of Arizona WESTCARB Phase III (California Energy Commission Agreement Number 500-10-024). The focus of this study is Cenozoic basin volume and volume below 800m depth, with the purpose of reducing the number of basins subjected to further carbon-sequestration evaluation. Basin volume below 800m depth is important because CO2 will remain in a liquid state at pressures corresponding to rock overburden at such depths. Successful sequestration requires both adequate permeability and porosity for large-volume CO2 injection, and an impermeable cap rock that will prevent movement of CO2 to shallower depth and escape to the atmosphere. Basin stratigraphy and sediment characteristics are not the subject of this report, however, but will be evaluated for a subset of basins identified in this study that are both large and deep.