When a riser is damaged, the oil spills to sea. Oil spills cause huge economic losses as well as a destruction of the marine environment. To reduce losses, it is needed to predict spilled oil volume from risers and the excursion of the oil. The present paper simulated the oil spill for a damaged riser using open source libraries, called OpenFOAM. To verify numerical methods, jet flow and Rayleigh-Taylor instability were simulated. The oil spill simulated for various damaged leak size, properties, damaged vertical locations of a riser, and current speeds. From results, the maximum excursion of the spilled oil at the certain time was predicted, and a forecasting model for various parameters was suggested.