Cargo ships and vessels transit the Bosphorus Strait, a body of water connecting the Black Sea to the Marmara and Mediterranean Seas through Istanbul, Turkey.
Above, the Russia-flagged vessel Volga River Taganrog oil tanker passes south through the Bosphorus Straits in October 2022.
"It appears that all but one of the roughly twenty loaded crude tankers waiting to cross the straits are carrying Kazakh-origin oil," a price cap official told CNBC.
If delays mount, refiners will seek alternative supplies from other countries or they will reduce operating capacity because they don't have enough oil, which impacts the supply of gasoline and diesel, said Andrew Lipow, president of Lipow Oil Associates.
"If this continues for another week we will begin to see an impact on the oil market," Lipow said.