Routine operation of production platforms leads to the release of oil, chemicals and naturally occurring radioactive materials to the sea, especially through discharges of produced water and partly from drill cuttings. Accidental oil spills can arise from different sources during operation. The main source of oil discharge from routine production is produced water. This is the water that comes from the reservoir along with the oil. Produced water contains hazardous substances occurring naturally in the reservoir, such as heavy metals, aromatic hydrocarbons, alkyl phenols and radionuclides. Produced water also contains residues of chemicals used in the production process, including corrosion inhibitors and demulsifiers (chemicals that increase the separation of oil from water). Drilling requires the use of fluids that may contain a range of chemicals.