The Coast Guard said it was trying to determine how many gallons may have been spilled into the river near Vicksburg, Mississippi.
The tank that was leaking contained 80,000 gallons of oil.
A Coast Guard team has stopped the source of the spill, the agency said in a news release.
The river is closed from mile marker 425 to 441.
No one was injured in the accident, which happened at 1:30 a.m.
The Mississippi River at Vicksburg moves about 890,000 cubic feet of water per second, according to the U.S. Geological Survey. If the vessel were to lose all its oil, that would be about 11,000 cubic feet.
In February 2012 a tanker barge spilled 10,000 gallons of oil into the Mississippi after a collision near New Orleans. The Coast Guard drained the barge and towed it to a repair facility.
CNN’s Chandler Friedman contributed to this report.