"Once we get that in hand, we'll get a better estimate of when the river will be reopened,"he added.
Tugs were holding the ruptured barge at the bank on the Louisiana side of the river, directly across from Vicksburg's Riverwalk and Lady Luck casinos.
Both of the barges involved are owned by Corpus Christi, Texas-based Third Coast Towing LLC, Lt. Gomez said. A woman who answered the phone at the company Monday declined to comment.
Both vessels were being pushed by the tug Nature's Way Endeavor. The website for Nature's Way Marine LLC of Theodore, Ala., identifies the vessel as a 3,000-horsepower, 90-foot-long boat. It was built in 1974 and underwent a rebuild in 2011, according to the company.
A company manager referred calls to the Coast Guard in Vicksburg.
Authorities said United States Environmental Services, an oil spill response company, was collecting oily water.
Officials did not yet have an estimate of how much oil had been pumped out, or how much spilled into the Mississippi.
"There's a list to the barge the way it's sitting. You can't get an accurate reading," said Lally.
But he said the oil was contained and skimmers would work nonstop.
Drew Smith, a hydraulic engineer with the Army Corps of Engineers, wouldn't speculate on the specific cause of Sunday's crash, which is under investigation by the Coast Guard. But he said the Mississippi at Vicksburg is challenging for southbound vessels, mostly barges carrying grain and other products from the nation's heartland.
Southbound tows must travel faster than the flow of the water for their rudders to steer effectively. At Vicksburg they must negotiate a 120-degree turn on the meandering Mississippi, then straighten up to pass under the railroad bridge and the Interstate 20 bridge.
The task is made more difficult by the Yazoo River, which empties into the Mississippi north of the bridges, increasing the speed of the current.
Associated Press writers Janet McConnaughey in New Orleans and Bill Cormier in Atlanta contributed to this report.