A new method is proposed in this paper to detect oil slick signatures in oceanographic SAR images. This method is based on directional behavioural oil slick in the sea surface. Therefore, directional hysteresis thresholding responses are first computed in order to bring to the fore dark spots, and increase pixels connexity in each Freeman direction. Those responses are then merged with the help of a Context Independent Constant Behaviour (CICB) operator. The proposed method is tested on ERS SAR amplitude images of Mediterranean and Atlantic seas. The obtained results are promising and show a good qualitative detection.