NEW ORLEANS – A stretch of the Mississippi River at New Orleans could be closed for days as crews clean a 12-mile oil slick caused Wednesday when a tanker and barge collided, officials said.

Heavy, almost tar-like fuel oil spilled from the barge, forming the slick and closing about 47 miles of the river, the Coast Guard said.

The barge “was T-boned and split in half,” Coast Guard spokeswoman Lt. Cdr. Cheri Ben-Iesau said.

It held more than 419,000 gallons of fuel oil in three tanks. Investigators don't know whether all three tanks broke but “are assuming the worst-case discharge of all 9,980 barrels,” said Capt. Lincoln Stroh, Coast Guard captain of the port of New Orleans.

Ben-Iesau said a tugboat without a properly licensed pilot was pushing the barge; the person operating the boat had an apprentice mate's license. The operator's name wasn't immediately released. She said an investigation was under way.

The double-hulled tanker Tintomara was loaded with about 4.2 million gallons of biodiesel and nearly 1.3 million gallons of styrene, but did not leak, said Michael Wilson, president of ship management company Laurin Maritime (America) Inc. in Houston. Styrene is used to make plastics and rubber such as in automobile parts, shoes, drinking cups and other food containers

American Commercial Lines Inc. of Jeffersonville, Ind., which owns the barge, brought in four oil spill cleanup companies with about 200 people and 10,000 feet of boom to keep oil away from water intakes and environmentally fragile areas, said Paul Book, vice president of operations facilities.

State Department of Environmental Quality spokesman Rodney Mallett said the spill poses minimal risk to wildlife because environmentally sensitive areas have been boomed off.

Tugs held the two halves of the barge against the river's swift current.

It had just been filled at Stone Oil Co. in Gretna, across the river from the accident site, and was on its way to Memphis, said W. Norbert Whitlock, executive vice president of American Commercial Lines.

The tanker was fully manned with a crew of 22 and was heading downriver, said Wilson, who heads the U.S. subsidiary of Laurin Maritime AB of Goteborg, Sweden. The tanker is owned by Whitefin Shipping Co. Ltd. of Gibraltar, he said.

Neither company nor Coast Guard officials would comment about the investigation.