US scientists put out a new estimate last night of the flow rate of the BP oil disaster, and determined that almost five million barrels, or 200,000,000 gallons, of oil released out of the busted Macondo well since the explosion on April 20.

The scientific teams estimate that 53,000 barrels of oil per day were leaking from BP’s well immediately preceding its closure via the capping stack.

Recent measurements and modeling also show that, as a result of depletion of the hydrocarbon reservoir, the daily flow rate decreased over the 87 days prior to the well’s closure. Based on these measurements and modeling, the scientific teams estimate that, at the beginning of the spill, 62,000 barrels of oil per day were leaking from the well.

Overall, the scientific teams estimate that approximately 4.9 million barrels of oil have been released from the well. Not all of this oil and gas flowed into the ocean; containment activities conducted by BP under U.S. direction captured approximately 800,000 barrels of oil prior to the capping of the well.

This is over ten times the initial estimates of flow rate from BP at the outset of the disaster. And given the expected ruling of “gross negligence” leading to a $4,300 per barrel fine on BP, that comes to a total of about $21.2 billion in fines, just for the violations of the Clean Water Act, and not counting the punitive awards, cleanup costs, and other penalties the company will be forced to pay.

For those who think that the fine may be too great, given the magic disappearing oil and the relative bounce-back of the Gulf, here’s a reminder that any new substance introduced into a fragile ecosystem can end up disrupting the balance and destroying some marine life:

There’s a destructive liquid flowing into the Gulf of Mexico — and it’s not oil.

It’s the muddy freshwater of the Mississippi River, which has been released from southern Louisiana’s vast levee system and into estuaries in greater quantities than usual. The goal has been to use the rush of freshwater to keep sticky oil from reaching the sandy shores of the state.

The tactic has proved moderately successful in some areas, but the extra freshwater creates lower-than-normal salinity levels in Barataria Bay and Breton Sound, which flank the southeast portion of Louisiana that juts out into the gulf.

Some biologists are worried. Mass oyster deaths have been reported in those two areas, early evidence suggesting that the freshwater could be shaking up a delicate ecosystem and a struggling seafood industry — both already threatened by the largest offshore oil spill in U.S. history.

Those fines, at the root, must act as a deterrent. And $21 billion dollars, or BP’s entire profit for the calendar year 2008, may do the trick.