About 4,000 barrels of fuel spilled in the Houston Ship Channel during the weekend after two barges collided in Galveston Bay near the mouth of the Gulf of Mexico.
The U.S. Coast Guard said more than 90 vessels are waiting in line to regain access to the Port of Houston, which remains closed during the incident response.
"Once the channel has been determined safe to navigate, and transiting vessels will not spread oil contaminants, a prioritization list will be established to determine the entry order of vessels," it said in a late Monday update.
The Coast Guard said federal and state wildlife officials were on hand to care for bird species threatened by the spill. At least seven birds died as a result of being oiled and more than a dozen were reportedly affected.
"Air monitoring continues throughout the general area, although readings have consistently shown no reason for health concerns," the Coast Guard said.
More than 71,000 feet of containment boom were deployed to contain the spill, which has moved south toward the Gulf of Mexico.
Exxon Mobil said Monday the closure of shipping lanes forced it to shut down its regional refinery.
[U.S. Coast Guard]