An automatic, oil-spill-detection system, which employs thin-film and wavefront-splitting interference techniques to determines the existence of surface oil or oil drops in water is disclosed. Two independent automatic, decision-making systems are disclosed, which provide a reliable means for oil spillage detection. A computer code and a image extraction system are employed to discern and monitor the interference fringes generated from oil slicks. The computer-based imaging system can be further replaced by a compact and low-cost imaging circuit that functions reliably in a buoy with relatively low power consumption.