Vessels account for an estimated 81% of the annual ocean oil slick area that researchers could attribute to a source, according to a SkyTruth study reported by Splash 247. Merchant ships were the leading vessel types associated with the slicks, putting commercial shipping at the centre of the satellite-monitoring group’s findings on chronic marine oil pollution.
The analysis estimates that oil slicks cover about 1.58 million square kilometres of ocean surface each year. More than 90% of that coverage falls within national waters, frequently near coastlines, Splash 247 reported. Researchers combined Sentinel-1 radar images gathered from 2023 to 2025 with information from SkyTruth’s Cerulean monitoring platform to assess the extent of pollution and its links to vessels and offshore facilities.
The vessel-related findings encompass both ships visible through automatic identification system, or AIS, tracking and so-called dark vessels without visible tracking signals. Areas identified as pollution hotspots include the Red Sea, Persian Gulf, Mediterranean and Black Sea, alongside waters off West Africa and around Indonesia. The study also found that the flags of Palau, Panama, Malta and Cyprus appeared disproportionately often relative to their fleet sizes, raising questions about flag-state oversight.
At the individual ship level, researchers identified 16 vessels associated with slicks in more than 10% of the satellite passes in which they were observed. Several offshore facilities were also linked to slicks, particularly off Indonesia and Nigeria. The findings therefore associate the pollution with both mobile vessels and fixed offshore operations, although ships represented the largest share of attributable annual slick area.
Marine protected areas generally showed lower pollution levels: roughly 75% had lower slick concentrations than neighbouring waters. However, sensitive habitats in the Black Sea and Gulf of Mexico remained affected. SkyTruth also flagged limits to the assessment, with sparse satellite coverage leaving extensive high-seas areas poorly monitored. Opaque ship ownership structures were a further obstacle to accountability, the report said.