Refineries along the eastern U.S. coast imported approximately 850,000 barrels of crude oil per day on average from the North Sea and Africa.
The Energy Department's analytical arm, the Energy Information Administration, said about 210,000 bpd of so-called Forties crude was scheduled for August delivery. The EIA said Thursday that was "significantly lower" than the August average of 360,000 bpd for 2008-12.
The Forties crude oil type, along with Brent, Oseberg and Ekofisk, determine Brent crude prices, a global benchmark.
EIA said three deliveries of Forties crude oil scheduled in August were delayed one month. Regular maintenance for Forties crude is lasting longer than planned, it said.
"There have also been reported delays in scheduled Ekofisk September loadings, which could cause tightness in the Brent crude oil market to extend into next month," the administration said Thursday.
The EIA said a disruption to any one of the North Sea crude oil varieties could drive Brent crude oil prices and any of the other oil prices linked to the benchmark.