The sanctions imposed by the United States on two Russian oil giants have taken effect, risking tens of millions of barrels of Russian oil being stuck at sea.

The US sanctions took effect on Friday, potentially leading to nearly 48 million barrels of Russian crude oil stranded at sea, forcing dozens of oil tankers to seek alternative destinations, marking a new blow to global oil trade. Washington last month blacklisted Russian oil companies, Lukoil and Rosneft, in what can be considered the most aggressive action against Russia since this administration took office, as President Donald Trump tries to increase pressure on the Kremlin in the Russia-Ukraine conflict. The US Treasury Department earlier this week stated that these measures have been successful, as demand has decreased and the price of Russia's main oil has also fallen. The restrictions are now in effect, with Indian refiners seeking alternative supplies and booking tankers for Middle Eastern cargo at unprecedented speed, pushing freight rates on that route to the highest level in nearly five years. Meanwhile, traders are closely monitoring the ultimate buyers of the crude oil that Lukoil and Rosneft have been transporting at sea. "Russian exports remain steady, but have not reached their destinations yet," said Warren Patterson, head of commodities strategy at ING Groep NV. "If this situation continues, and all supplies end up being sent back, we could see a drop in supply, which would cause market concerns."