Numerical simulators were exercised on a suite of test problems for CO2 disposal in saline aquifers and depleting oil and gas reservoirs. Intercomparison of results reveals broad agreement in most areas, but also points out sensitivities to fluid properties and discretization approaches that need further study. Currently available simulation codes were shown capable of modeling the complex phenomena accompanying geologic storage of CO2 in a robust manner, and with quantitatively similar results. Published by Elsevier Ltd.