It was intended to confirm, based on various problems surrounding oil flow-out accidents, that oil fences whose use is first considered when an oil flow-out accident occurs cause oil leakage due to oil pass-through phenomenon as the largest defect in performance of oil fences. Therefore, oil fence performance was analyzed by using a simulation. Furthermore, several types of diffusion prevention and avoidance measures, and combinations thereof were evaluated by using multi-criteria analysis. It was also elucidated how recognitions on the importance of methods to prevent oil pollution differ depending on standpoints. Difference in oil flow-out prevention performance of oil fences due to variation in tidal currents was made clear by combining a diffusion simulation using the finite element method with the prevention performance of oil fences relative to the tidal currents. In areas with no good hydrographic conditions where pollution spreads rapidly, it is necessary to suppress oil diffusion by extending oil fences double or triple, and using gelling agents. 4 refs., 8 figs.