The U.S. Coast Guard is working to assess the total number of gallons of oil leaked off the coast of Southern California, as an investigation into the spill’s cause continues.

Preliminary findings estimate a minimum of 24,696 gallons, or 588 barrels, was released from a pipeline during the spill, according to Capt. Rebecca Ore, sector commander for the Los Angeles-Long Beach region. The maximum “worst case discharge” is 131,000 gallons, or 3,134 barrels of oil, she said at a press conference Thursday. Officials earlier estimated the spill totaled 126,000 gallons.

“We are working on a precise estimate,” Capt. Ore said, noting that five federal and state agencies worked to put together the current estimates. “I would expect that number to change… I wouldn’t expect it to change significantly.”

According to a group of organizations conducting spill-related operations, 5,544 total gallons of crude oil have been recovered as of Friday. An additional 172,500 pounds of “oily debris” have been recovered from shorelines.

The official cause of the spill remains under investigation. A spokesperson for the Coast Guard said the agency is looking into several vessels but won’t be releasing the names of the ships.

There were eight container ships and two tankers at anchor off the coast of Huntington Beach around the time of the incident, according to data from the Marine Exchange of Southern California.

An investigation into one of those vessels, a German container ship, has concluded, according to a spokesman for the German shipping company Hapag-Lloyd AG. The Coast Guard had boarded the Rotterdam Express Wednesday. The ship, which has a capacity of about 4,900 boxes, dropped its anchor Sept. 21 as it was asked and didn’t move or pass over the pipeline during the period in question, according to the spokesman.

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