According to Petty Officer Richard Brahm, the ship's crew members said they pumped 69,000 barrels from the damaged tank that carried 80,000 barrels, so they have 11,000 barrels -- about 450,000 gallons -- that they can't account for.
Several local officials said only 1,000 barrels, or about 42,000 gallons, of oil had been spilled into the water.
Brahm acknowledged that it doesn't look like hundreds of thousands of gallons of crude was in the water. He said some might still be in the damaged tank.
"We can't get in there and look at it," he said.
Port Arthur police Sgt. Ken Carona told television station KFDM that fewer than 100 people were evacuated from the area. He said hydrogen sulfide -- a hazardous gas with a rotten egg smell -- was emanating from the oil. He told the station that the levels aren't hazardous, but are a nuisance.
Greg Fountain, the Jefferson County emergency management coordinator, said he expects to evacuation order to be lifted once the vessels are separated, but he wasn't sure when that would happen. He said they'll wait till then because there is the risk of an explosion when the two metal vessels are separated.
"You never know where a fire source might come from," said Fountain, who said that a shelter was set up for evacuees at the city's recreation center.
Fire department spokeswoman Angell Thibodeaux said a 28-block area downtown was evacuated.
Coast Guard Petty Officer Renee Aiello said the crude spilled when an 800-foot tanker carrying oil collided with a towing vessel pushing two barges. The Coast Guard was notified of the collision around 9:50 a.m., she said.
The crash left a 15-by-8-foot hole in the tanker, Aiello said. The towing vessel then hit another tanker that was tied to a pier. Brahm said that tanker sustained some damage, but had no leaks.
Brahm said the Coast Guard, which is in charge of the cleanup, had contained the spilled oil with floating plastic barriers.
Port Arthur is about 90 miles east of Houston.
The damaged tanker, the Eagle Atome, is owned by AET Tankers, according to the Houston Chronicle. AET is a Malaysian company with offices in Houston.
The Port Arthur spill is much smaller than the 11 million gallons spilled in Prince William Sound when the Exxon Valdez ran a ground in 1989.
One of the worst shipping accidents in the area was the June 1990 spill from the Norwegian tanker Mega Borg. It leaked 4.3 million gallons of crude oil about 60 miles off Galveston.