This paper proposes the method of examining the performance from recent experimental results about oil-interceptors. According the results, the oil keeping performance against to rain water and a large amount of oil inflow clearly can manipulate by using a few types of internal mechanics of oil-interceptors. The test condition and the measuring method for which good retention efficiency on sand and oil and the rise in water level are presented here. As a result, the relevant selection of oil-interceptor that has the proper capacity and mechanics becomes available.