What is Iran's shadow fleet via which it makes $30 bn annually?

Iran's shadow fleet is a collection of oil tankers used by Iran to bypass global sanctions and continue exporting crude oil. The fleet, overseen by Iran's Islamic Revolutionary Guard Corps (IRGC), consists of around 400-450 vessels, according to a report by CNN-News18. The fleet reportedly generates 25-30 billion annually and much of the crude oil is purchased by China.