Staring day after day at images of oil billowing from an undersea well in the Gulf of Mexico, many Americans are struggling to make sense of the numbers.

On Monday, BP said a cap was capturing 11,000 barrels of oil a day from the well. The official government estimate of the flow rate is 12,000 to 19,000 barrels a day, which means the new device should be capturing the bulk of the oil.

But is it? With no consensus among experts on how much oil is pouring from the wellhead, it is difficult — if not impossible — to assess the containment cap’s effectiveness. BP has stopped trying to calculate a flow rate on its own, referring all questions on that subject to the government. The company’s liability will ultimately be determined in part by how many barrels of oil are spilled.

The immense undersea gusher of oil and gas, seen on live video feed, looks as big as it did last week, or bigger, before the company sliced through the pipe known as a riser to install its new collection device.