In this study the capability of the co-polarized phase dif- ference (CPD) for oil spill observation has been investi- gated. A simple and effective filtering technique, based on the standard deviation (σ) of the CPD Synthetic Aper- ture Radar (SAR) image, has been implemented. First experiment, accomplished over SIR-C/X-SAR C-Band data, have shown different sensitivity of the filtering tech- nique with respect to oil spills and biogenic oil look- alikes. Since this technique needs only HH and VV data it can be applied also on dual-polarized data such as those provided by the ASAR operated on board on the ENVISAT satellite and the forthcoming COSMO- SKYMED.