Iranian crude exports to China have been disrupted by broader US sanctions on tankers, according to Vortexa Ltd., squeezing oil flows to the OPEC producer’s most important customer.

Some November cargoes remain undelivered, following disruptions to a number of October shipments, Emma Li, a senior market analyst, wrote in a note. At least 191 Very Large Crude Carriers are on the US sanctions list, according to Vortexa.