Tens of millions of gallons of oil have leaked into the Gulf of Mexico, but that's only about 1 to 1.5 percent of what sits in the reservoir deep beneath the ocean floor, according to calculations based on government and BP estimates.

A government analysis released on Thursday placed the daily rate of oil entering the Gulf at somewhere between 12,000 and 19,000 barrels. (One barrel contains 42 gallons.) That range, announced by the head of the U.S. Geological Survey, was based on three analyses conducted by a team of government experts, independent experts, and professors.

If the estimates are correct, the Gulf leak has spilled more oil into the ocean than the 1989 Exxon Valdez oil tanker spill. A total of 468,000 to 741,000 barrels would have leaked as of the end of the day Friday, 39 days after the April 20 explosion that caused the leak. The 1989 Exxon Valdez oil tanker spill spilled 257,000 barrels.

BP's Gulf well stems from the Macondo oil prospect, a reservoir located roughly 18,000 feet below sea level, or 15,000 feet below the ocean floor. The prospect was estimated to have contained 50 million barrels before the explosion, a BP spokesman said earlier this month.

Calculations based on the BP and government estimates reveal that somewhere between 0.94 and 1.48 percent of the Macondo reservoir has been depleted.

Tulane University Professor Eric Smith cautions that the 50 million barrel figure is not a terribly good estimate, though. BP's well was a preliminary "discovery well," said Smith, who is also an associate director at the Tulane Energy Institute. And calculating the amount of oil in the reservoir is difficult: "it's a geometry problem to define what the enclosed volume is."

Left unattended, the Macondo prospect would fully deplete because the pool of oil sits under the weight of thousands of feet of ocean and rock, he said: "The earth is providing the pressure."