New Delhi, Jan. 20 -- With the US's recent invasion of Venezuela, and sanction and tariff threats on trade with Iran, the so-called global 'shadow fleet' of oil tankers is in focus again.

Used to transport oil by countries under Western sanctions such as Russia, Iran and Venezuela, the size of this fleet has grown manifold and now accounts for an estimated 18.5% of global tanker capacity, according to S&P Global.

It's called a shadow fleet because it uses various methods to evade detection by sanctions-enforcement agencies, such as frequently changing the name of the ship and its flag (the country where it is registered), and turning off its transponder to make it invisible to GPS satellites.

The shadow fleet came into its own followin...