Conservation group SkyTruth estimates oil slicks cover about 610,000 square miles of ocean each year, an area far larger than the tanker disasters that usually make the news.
The Sept. 23 analysis draws on the group’s Cerulean platform and Sentinel-1 radar images from 2023 through 2025. It maps chronic slicks tied to ships and offshore oil equipment, not only rare blowouts. The raw figure is 1.58 million square kilometers, or roughly 610,000 square miles. More than 90 percent of the estimated pollution falls inside national waters, often near coasts. High-seas coverage is thinner, so the true open-ocean total is incomplete.
About 81 percent of slick area that could be tied to a source is associated with vessels, including ships that broadcast AIS positions and so-called dark vessels that do not. Tankers and cargo ships dominate that group.
“Oil pollution is a constant, global issue that happens far more often than the spills that make headlines. We’ve now estimated its true scale using satellite data — the problem is measurable, and potential sources can increasingly be identified. Our analysis also reveals where the biggest gaps in accountability and protection remain, and that is where attention and enforcement need to be directed,” said Karl Wuster, Chief Technology Officer at SkyTruth.
© SkyTruth
Hot spots include the Red Sea, Persian Gulf, Mediterranean and Black Sea, waters off West Africa and seas around Indonesia. About 75 percent of marine protected areas show lower slick density than nearby waters. Exceptions remain. SkyTruth flags porpoise and dolphin habitat in the southeast Black Sea and Rice’s whale habitat in the Gulf of Mexico.
Fleets under flags including Palau, Panama, Malta and Cyprus appear more often in the slick data than their fleet size alone would suggest. Sixteen individual ships show up with slicks in more than 10 percent of observed satellite passes. Several offshore platforms, especially off Indonesia and Nigeria, also recur. Beneficial-ownership records are often thin, the group said, which makes it hard to name the companies behind those ships.
Association is not a courtroom finding. Radar can miss slicks and can also pick up look-alikes. SkyTruth released the report during Climate Week NYC and plans a webinar on Sept. 30. The nonprofit uses satellite imagery to document environmental harm for governments and researchers.
