Just judging by the size of the slick — about 3,500 square miles — and the three weeks of the spill, 210,000 “looks about right as far as the slick goes,” Fischbeck said.

If the higher estimates were right, there would be a much bigger slick, he said.

But some of the oil could be lingering under the water’s surface. In previous cases, it’s been as much as half of the spill, said University of California Berkeley engineering professor Bob Bea.

The environmental impact will be vastly different depending on the size of the spill, some experts agreed.

If the flow turns out to be closer to the higher end estimates, “that’s a major catastrophe,” Bea said. If it’s closer to the government’s estimate, it is something that can be handled.