He made a few simple calculations and came up with an astonishing value for the rate of the oil spill: 70,000 barrels a day -- much higher than the official estimate of 5,000 barrels a day.
The method is accurate to a degree of plus or minus 20 percent.
The New York Times adds another wrinkle:
The figure of 5,000 barrels a day was hastily produced by government scientists in Seattle. It appears to have been calculated using a method that is specifically not recommended for major oil spills.
The original government estimate for the size of the spill was a mere 1,000 barrels per day. That was adjusted to 5,000 per day over a week after the explosion that brought down the Deepwater Horizon.