The principal environmental impact of the exploitation of oil and gas on the Netherlands Continental Shelf (NCS) is associated with the discharge of cuttings containing residues of oil containing drilling mud and of oil containing production water. In 1986, these discharges amounted to a total of about 4,700 tons of oil being discharged into the sea, that is about one quarter of the oil discharged by all the platforms in the North Sea. The results of monitoring round locations on the NCS where drilling operations took place before 1987 lead to conclusions which correspond with British investigations in the southern part of the North Sea.
Elevated oil concentrations in the sediments are found at distances of up to 750–1000 metres from the drilling locations. Within a distance of 50–250 metres, concentrations occur of 100 to 10,000 times the background level. In these areas, distinct effects on the seabed fauna are also noticeable: a substantial reduction if not a total disappearance of the sea-bed fauna can be observed.
The oil pollution is not distributed homogeneously: as a result of water currents and of spread caused by sea bottom fishing, a patchy pattern has been created.