The dark fleet of tankers shipping illicit oil around the world is rushing to seek the perceived protection of the Russian flag after the U.S. started seizing vessels involved in the Venezuelan trade.

With five oil tankers seized—and more U.S. military action promised—the world’s fleet of so-called shadow tankers that ferry sanctioned crude are quickly hoisting a new flag: the Russian tricolor.

WASHINGTON (AP) — The United States seized two sanctioned oil tankers linked to Venezuela in back-to-back actions in the North Atlantic and the Caribbean Sea, officials said Wednesday, and is removing ...