The 1.6 million visitors a year to the USS Arizona Memorial are told by their guides about the legends surrounding the oil that still bubbles up from the sunken battleship.

One legend holds that the oil represents the tears of the 900-plus sailors and Marines entombed below decks since the Japanese attack of Dec. 7, 1941. Another says the oil will continue to surface until the last Arizona survivor dies.

But the fact is that 500,000 or more gallons of fuel oil are estimated to remain aboard the Arizona. Now the National Park Service and the Navy, which jointly maintain the memorial, are in the early stages of a comprehensive study of the ship and the possibility that its oil might someday spill into Pearl Harbor, fouling the shoreline and hampering naval operations.

When 100,000 gallons of jet fuel spilled from a pipeline in 1987 — unrelated to the Arizona — it disrupted the Navy base here for two months.

A 2005 report for the Park Service said a spill of 500,000 gallons from the Arizona "may be catastrophic."

Though the scientific consensus is that such a spill is unlikely, the National Oceanic and Atmospheric Administration's Office of Response and Restoration late last year updated its emergency plan just in case.

"It's a far more complex situation than we ever imagined," said James P. Delgado, a noted shipwreck explorer and the executive director of the Institute of Nautical Archaeology. He wrote a 1989 report that led to the Arizona's being named a national landmark.

A day before the attack that plunged America into World War II, the Arizona had taken on 1.2 million gallons of fuel oil.

Much of it spilled into the water after an armor-piercing bomb from a Japanese warplane struck the battleship's forward magazine.

An enormous explosion lifted the ship out of the water.

It sank within nine minutes — the time it now takes a Navy launch to transport people from the Arizona Memorial Visitors Center to the memorial, which bestrides, but does not touch, the ship.

As part of the Park Service study, computer modeling at the National Institute of Standards and Technology — using data from divers and remote-control cameras — aims to see how the oil may be moving inside the wreckage and how soon corrosion may collapse the steel hull, allowing the oil to push to the surface.

Preliminary results suggest the oil movement is modest and corrosion has been slowed by the mud at the bottom of the harbor, said Timothy Foecke, a metallurgist at the institute.

Delgado believes the study on the Arizona will provide a key to the future of the hundreds of other ships sunk during World War II and how soon oil inside those ships may escape into the water.

Although the oil may — or may not — pose a serious environmental risk, there is no disputing that for many, it adds to the memorial's emotional power.

Visitors walk the 184-foot-long memorial and scan the "shrine room" wall that contains the names of the 1,177 men who were killed aboard the Arizona. Many visitors stare down at the rusted remains of Gun Turret 2 and the small rainbow-colored ringlets of oil that reach the surface — several quarts a day.

"When people see and smell the oil, they're brought back to the world of Dec. 7," said Daniel Martinez, the Park Service historian at the memorial.

"The oil is a reminder that the Arizona is a wounded and dying ship."

The public attachment to the Arizona and the memorial also poses problems regarding the oil, experts said.

For any other wrecked ship, punching holes in the hull and pumping out the oil would be relatively easy, particularly for a ship that is so close to land and sits in only 40 feet of water. But for the Arizona, such an idea is considered unthinkable, except as a last alternative.

Along with being told the legends, visitors are assured that nothing so intrusive will happen to the Arizona.

Actor Ernest Borgnine, who served in the Navy during World War II, is the narrator of a self-guided audio tour that visitors can rent at the visitors center. Near the end of the tour, Borgnine says many people believe that "to remove the oil would be to desecrate the tomb."

When the Park Service approaches the wreckage, it makes sure to discuss its plans with the USS Arizona Reunion Assn., a survivors group.

"We are very, very conscious of the sanctity of the Arizona," Martinez said.