42,000 gallons per day

And it's been three days.

For days, the Coast Guard has said no oil appeared to be escaping from the well head on the ocean floor. Rear Adm. Mary Landry said the leak was a new discovery but could have begun when the rig sank on Thursday, two days after the initial explosion.

"We thought what we were dealing with as of yesterday was a surface residual (oil) from the mobile offshore drilling unit," Landry said. "In addition to that is oil emanating from the well. It is a big change from yesterday ... This is a very serious spill, absolutely."

Coast Guard and company officials estimate that as much as 1,000 barrels -- or 42,000 gallons (160,000 liters)-- of oil is leaking each day after studying information from remotely operated vehicles and the size of the oil slick surrounding the blast site. The rainbow-colored sheen of oil stretched 20 by 20 miles (30 by 30 kilometers) on Saturday -- about 25 times larger than it appeared to be a day earlier, Landry said.

By comparison, Exxon Valdez spilled 11 million gallons (40 million liters) in Alaska's Prince William Sound in 1989 -- the worst oil spill in U.S. history.