Figure 1. US Coast Guard map showing size and appearance of oil slick on April 28, 2010.

Dr. Ian MacDonald at FSU just produced a new spill-size estimate based on the US Coast Guard aerial overflight map of the oil slick on April 28, 2010. This map shows the slick covering 1,786 square miles (4,627 square kilometers). The bottom line: on April 28 there was a total of 8.9 million gallons floating on the surface of the Gulf.

That suggests a minimum average flow rate of slightly more than 1.1 million gallons of oil (26,500 barrels) per day from the leaking well on the seafloor. Since we’re now in Day 11 of the spill, which began with a blowout and explosion on April 20, we estimate that by the end of the today 12.2 million gallons of oil, at a minimum, have been spilled into the Gulf of Mexico.

The oft-quoted official estimate for the Exxon Valdez spill is 11 million gallons, although some think that is the lower limit of the likely range. It appears that we’ve just set a very sad new record.