New satellite analysis estimates oil slicks cover 1.58 million km² of ocean surface each year

SkyTruth today released a new global analysis estimating that 1.58 million km² of ocean surface is covered by oil slicks each year.

More than 90 per cent of the estimated pollution occurs within national waters, often near coastlines. But limited satellite coverage, particularly on the high-seas, leaves substantial areas of the ocean unmonitored, creating a significant observability gap in understanding chronic marine pollution. Approximately 81 per cent of the attributable annual oil slick area is associated with vessels, including AIS-tracked and ´dark´ vessels, while tankers and cargo vessels are the dominant vessel types associated with the slicks.

“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.

Key findings offer a new way to investigate chronic marine pollution beyond major spills. By combining satellite imagery with data from SkyTruth’s Cerulean platform and Sentinel -1 radar imagery collected between 2023 and 2025, the analysis provides a global picture of where chronic oil pollution is concentrated and identifies potential sources for further investigation.

Key Findings

• Pollution is concentrated around major maritime and oil-producing regions

Some of the highest concentrations are found in the Red Sea, Persian Gulf, Mediterranean, and Black Sea, off the western coast of Africa and in waters surrounding Indonesia.

• Marine protected areas generally have lower slick concentrations – but significant exceptions remain

Around 75% of marine protected areas have lower slick concentrations than surrounding waters. However, sensitive marine mammal habitats remain affected by oil pollution – including porpoise and dolphin habitat in the Southeast Black Sea, and critically endangered Rice’s Whale habitat in the Gulf of Mexico.

• Several flags of convenience are disproportionately associated with oil slicks

Fleets operating under flags including Palau, Panama, Malta and Cyprus are disproportionately associated with slicks relative to fleet size. The findings raise questions about flag-state oversight and monitoring.

• A small number of vessels appear repeatedly in satellite observations of oil slicks

The analysis identified 16 individual vessels that appear to be associated with oil slicks in more than 10 per cent of observed satellite passes, alongside several offshore facilities, particularly off Indonesia and Nigeria.

The analysis also examines vessel ownership and corporate accountability, finding significant gaps in beneficial-ownership information that can make it difficult to identify the companies ultimately connected to vessels associated with chronic oil slicks.

The report is being released during Climate Week NYC, alongside SkyTruth´s event Turning Geospatial Data into Action on Pollution and Climate on September 23 in New York City. The event brings together leaders working on ocean pollution, offshore oil and gas emissions, and impacts of industrial activity on biodiversity. SkyTruth experts will be available to discuss the findings and methodology with journalists attending the event.

SkyTruth will host an online webinar on 30 September to discuss the report´s findings, methodology, and impacts. The webinar will provide an opportunity to hear directly from SkyTruth’s Chief Technology Officer and ask questions about the analysis. Please register here.

Source: SkyTruth