CDISCO, a Microsoft Excel spreadsheet–based model, can be used to assist with the design of in situ chemical oxidation (ISCO) systems using permanganate (MnO4). The model inputs are the aquifer characteristics (porosity, hydraulic conductivity, effective aquifer thickness, natural oxidant demand, kinetic parameters, contaminant concentrations, etc.), injection conditions (permanganate injection concentration, flow rate, and duration), and unit costs for reagent, drilling, and labor. MnO4 transport in the aquifer is simulated and used to estimate the effective radius of influence (ROI) and required injection point spacing. CDISCO then provides a preliminary cost estimate for the selected design conditions. The user can perform multiple runs of CDISCO to optimize the cost of the ISCO design. Comparisons with analytical and numerical models of nonreactive and reactive transport demonstrate that CDISCO accurately simulates MnO4 transport and consumption. Comparison of CDISCO results with the three-dimensional heterogeneous simulations show that aquifer volume contact efficiency and contaminant mass treatment efficiency are closely correlated with the ROI overlap factor. © 2011 Wiley Periodicals, Inc.