The latest round of sanctions has caused Iran to come up with a number of new methods to get around these prohibitions. Iranian agents are offering deep discounts to buyers willing to create false documents and move the Iranian crude. Selling oil at discounts of 30 percent or more still costs Iran. So also does the expense of secretly buying tankers that will pretend to belong to another country while moving the black market oil. While Iran has been successful in the past, that was because it was often moving items (like weapons components) that could be hidden in a cargo container. Oil is another matter. Iran has experimented with using shipping containers to smuggle oil but this is very inefficient and you can still get caught. Iran fears that between the CIA (photo satellites and spies) and the maritime insurance industry (that monitors world shipping via transponders and other sightings) it will be very difficult to move the illegal oil. This led Iran to come up with ways to confuse the international ship tracking system. These "maritime security technologies" were developed as a safety feature, and have proved valuable providing the positions of ships caught in storms or taken by pirates. AIS (Automated Identification System) and INMARSAT (International Maritime Satellite) were originally developed to make it easier for ships to track other nearby ships at sea. It enables shipping companies keep track of their vessels, no matter where they are on the planet. These two systems are now required by law (international agreements) for all sea going vessels greater than 300-tons. The technology has worked, and the U.S. Navy has found them particularly useful in counter-terror operations. Coast Guards the world over have also found the systems a big help. Iran often just has two ships trade INMARSAT IDs while they are near each other, leaving the U.S., or anyone else checking INMARSAT data, unable to track ships that have been switched.
But apparently pirates in some areas have gained access to the systems (via bribes or theft) and an increasing number of pirate attacks appear to have been helped by technology meant just to safeguard ships at sea. Iran, and other nations involved in smuggling learned how to have INMARSAT send a false signal, concealing where the ship actually is. This can work for a while, but a nation with lots of recon satellites, warships and cooperation from most of the world's shipping, can get around this. The Iranians are aware of the satellites and other means of double-checking transponder data and is constantly coming up with schemes to confound the American snoopers. Since Iran has been under sanctions for decades for being an outlaw state, threatening more punishment is seen as a challenge not a threat.