Venezuela has shipped out about a dozen oil tankers carrying crude and petroleum products in recent days, with vessels departing in dark mode, TankerTrackers.com said on Monday. All these tankers that have stealthily left Venezuela have been sanctioned by the U.S. Treasury, according to TankerTrackers.com data cited by Reuters. The dozen or so departures have taken place despite the U.S. blockade off Venezuela, which is aimed at preventing sanctioned tankers from going to and from the South American country. It was not immediately clear…