An oil slick spanning about 45,000 square kilometres off the coast of Iran's main crude export site has been detected by satellite imagery, but Tehran claimed the spill did not originate from the country's infrastructure.
The oil, visible in images captured by the Copernicus Sentinel-1, Sentinel-2 and Sentinel-3 satellites between May 6 and 8, appeared as a grey-and-white slick west of Kharg Island, which handles the bulk of Iran's crude oil exports in the Gulf.
Iranian Vice President Shina Ansari said the slick was caused by a tanker from another country dumping ballast water contaminated by oily substances, rather than a leak from Iranian pipelines or oil facilities, state media reported.
Satellite imagery analysts have told The National that they believe the leak is from a tanker, but warned the source could not be confirmed from optical imagery alone.
Reuters, which first reported the spill, said it covered an area of about 45 square kilometres based on the Copernicus data. While significant in the context of the current maritime crisis in the Gulf, the slick is considerably smaller than past spills in the region, including the 1983 Nowruz oilfield incident and the 1991 Gulf War discharge.
A slick of this size near Kharg Island risks affecting fisheries, coastal communities, desalination plants and marine habitats, experts said.
Kharg Island accounts for the vast majority of Iran's crude oil exports and the waters to its west are heavily used by tankers involved in loading operations. The location of the slick is consistent with that operating environment, but its proximity to the Kharg terminal does not establish it as the source, said Prof Hidenori Watanave, of the University of Tokyo, who analysed the imagery.
“The spatial pattern of the anomaly, a broad, drifting slick to the west and south-west of the island, appeared consistent with material carried by wind and current after a single release event, rather than a continuing leak from a fixed point on the seabed or shoreline. Later imagery did not show signs of an active, continuing discharge.”
Prof Watanave said the "available evidence points more towards a vessel-related discharge or leakage than a confirmed terminal or pipeline leak".
A rupture in an undersea pipeline connecting Kharg Island with the Abuzar oilfield, a major Iranian offshore site to the west, was also identified as a possible source of the slick. The pipeline is decades old, poorly maintained and has suffered several leaks in recent years, including a breach in October 2024, Prof Watanave said.
Other analysts have suggested that oil may have been deliberately discharged in the Gulf because of a lack of storage capacity, although there is currently no evidence to support that theory.
Independent verification would require radar satellite data and vessel movement records, as well as wind and current-backtracking analysis, Prof Watanave added. The incident highlighted how sanctions, conflict and chronic underinvestment in Iran have affected its oil infrastructure.
