An oil slick covering around 45,000 square kilometres of sea near Iran's main crude export centre has been detected by satellite imagery, but Tehran said the spill did not originate from local infrastructure.
The patch, visible in images captured by Copernicus's Sentinel-1, Sentinel-2 and Sentinel-3 satellites between May 6 and 8, appeared as a grey-and-white slick west of eight-kilometre-long Kharg Island, that handles the bulk of Iran's Gulf crude oil exports.
Iranian Vice-President Shina Ansari said the spill was caused by a non-Iranian tanker dumping ballast water contaminated by oily substances and denied that any leak had come from Iranian pipelines or oil facilities, state media reported.
However, satellite imagery analysts have told The National they believe the leak is from a tanker, but cautioned that the source could not be confirmed from optical imagery alone.
Reuters, which first reported the spill, said it covered an area of approximately 45 square kilometres based on the Copernicus data. While significant in the context of current Gulf maritime risk, the slick is considerably smaller than major historical spills in the region, including the 1983 Nowruz oilfield incident and the 1991 Gulf War discharge.
A spill of this size near Kharg Island risks affecting fisheries, coastal communities, desalination plants and Arabian Gulf marine habitats, experts said.
Kharg Island accounts for the vast majority of Iran's crude oil export capacity, and the waters to its west are heavily used by tankers involved in loading operations. The location of the anomaly is consistent with that operating environment, but proximity to the terminal does not establish it as the source, said Prof Hidenori Watanave, director of The University of Tokyo's III and GSII laboratories and deputy director general, 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 this was not an anomaly in a random part of the Gulf.
“It appears in a maritime zone directly connected to crude export activity. 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, a major Iranian offshore field to the west, was also identified as a possible source. The pipeline is decades old and poorly maintained, and has suffered several leaks in recent years, including a breach in October 2024, said Prof Watanave.
Other analysts have speculated that oil may have been deliberately discharged at sea because of a lack of storage capacity, although there is no evidence to support that theory.
Independent verification would require radar satellite data, vessel movement records, and wind- and current-backtracking analysis, said Prof Watanave.
The incident highlighted how sanctions, conflict and chronic underinvestment have made it increasingly difficult for Iran to modernise, maintain and replace critical oil infrastructure.
