The Response Options Calculator (ROC) is a project currently in development at Genwest. This software tool is designed to improve training and response capabilities for oil spills by guiding in the selection and assessment of response countermeasures during spill exercises and events. The ROC unifies logic from three existing NOAA Spill tools originally developed at Genwest: the Mechanical Equipment Calculator (MEC), which is a software tool for estimating performance in collecting and removing oil via booms and skimmers (vessels equipped to ‘skim’ oil off the water’s surface), the In-Situ Burn Calculator (ISB), which is program for estimating performance in collecting and burning oil in a specified length of fire boom and the Dispersant Mission Planner 2 (DMP2), which is a tool for planning the use of oil dispersants applied by aircraft and/or vessels. All three of these programs are encounter-rate models, they depend on a specification of an average thickness of oil, a system swath, and a speed of advance.  Finally, the ROC adds a capability to model oil weathering which provides an estimate of oil thickness for the encounter-rate models and other weathering information including evaporation, natural dispersion, emulsification, density, viscosity, and Langmuir cells.  One product provided by the ROC tool will be an oil mass-balance diagram which displays changes in spill volume over time to environmental effects such as evaporation plus oil recovered/removed/treated by oil spill countermeasures.