De-oiling of petroleum wastewater is a major concern in petroleum process engineering. Decision support systems (DSS) have been used in assisting operators in evaluating different disposal options of production water, but not the de-oiling process. Also, no application has been reported in assisting the de-oiling of other petroleum waters such as process, ballast or drainage water. This paper describes a DSS for the COnceptual DEsign of de-oiling Systems (CODES) for handling different types of waste water by supporting the tasks of:

–	assessing the types and magnitudes of waste-water streams
–	exploring the feasibility of mixing different streams.
–	selecting the types of de-oiling equipment at different stream locations
–	considers the need for multi-stage treatment to meet quality requirements stated in standards and regulations.