A large fleet of oil tankers used to export Russian crude oil is grinding to a halt, potentially as a result of increased U.S. sanctions on the Russian oil market, Bloomberg reported on Feb. 13. Nearly half of the 50 tankers sanctioned by the U.S. Treasury back in October have not loaded cargo since they appeared on tracking sites. The most recently impacted fleet, the Sovcomflot carrier NS Leader, was reportedly forced to turn around off the coast of Portugal when its owner was sanctioned by the U.S. while en route to the Russian port on the Baltic Sea. According to Bloomberg, 14 tankers carr…