An energy analytics firm said it recorded 34 movements of sanctioned and Iranian-linked tankers in and out of the Gulf in the week after the US imposed a naval blockade.
Vortexa said it identified 19 outbound and 15 inbound movements between April 13 and Monday.
Six outbound tankers were confirmed to be carrying Iranian crude, totalling about 10.7 million barrels.
It remains unclear whether all the shipments reached international markets.