For most of the war, Iran had an invaluable cushion: dozens of oil tankers holding millions of barrels of crude sitting safely in waters in Asia. Tehran steadily sold the oil to China, bringing in billions of much-needed cash.

Now, that floating storage is gone. By mid-October, the reserves were fully depleted, according to analysts at Kpler, as a U.S. naval blockade prevented Iran from replacing the crude it normally sells to Chinese refineries.