China’s crude oil purchases reported as originating from Indonesia have jumped sharply this year, a development that market analysts believe may reflect efforts to obscure the flow of Iranian barrels into the country.

Customs figures from Beijing show crude supplies declared from Indonesia soared to nearly 10 million tonnes between January and October — a volume far beyond Indonesia’s actual export levels. Indonesian data indicates only a fraction of that amount left the country’s ports, with minimal direct deliveries recorded to China.

Traders and analysts say the mismatch suggests Iranian crude, which is restricted under U.S. sanctions, is being reclassified as Indonesian after being transferred between tankers in Southeast Asian waters. Malaysia has long been the main location for these ship-to-ship transfers, but stricter monitoring from July prompted sellers to look for alternative declared origins, they said.

Market participants note that some banks have grown more cautious about documents showing Malaysian origin, increasing the incentive to reroute or relabel cargoes. Indonesia’s growing cooperation with the United States on energy and planned refinery projects has also made it a more palatable cover for shipments, according to consultants.

Despite the shift in paperwork, analysts say most transfers involving suspected Iranian oil continue to occur off Malaysia’s coast. Data from Kpler indicates China received more than 57 million tonnes of Iranian or Iranian-linked crude during the first ten months of the year, the majority moved through ship-to-ship operations.

Officials in China, Indonesia, and Malaysia did not respond to requests for comment on the unusual trade flows.