Not as bad as it could be, according to the NY Times,
The ruptured well, currently pouring an estimated 210,000 gallons of oil a day into the gulf, could flow for years and still not begin to approach the 36 billion gallons of oil spilled by retreating Iraqi forces when they left Kuwait in 1991. It is not yet close to the magnitude of the Ixtoc I blowout in the Bay of Campeche in Mexico in 1979, which spilled an estimated 140 million gallons of crude before the gusher could be stopped.
And it will have to get much worse before it approaches the impact of the Exxon Valdez accident of 1989, which contaminated 1,300 miles of largely untouched shoreline and killed tens of thousands of seabirds, otters and seals along with 250 eagles and 22 killer whales.
These comparisons may be a little misleading — a bit like saying that we shouldn’t worry about 9/11 because a a hundred times more people died in the Battle of the Somme in World War I. Something can be very serious without being “the worst ever.” Also, the total amount of harm isn’t just a function of the size of the spill or the amount of direct impact — the Gulf Coast ecosystem is already under tremendous stress, and this blowout could be a tipping point. Still, it’s worth putting this event in perspective.