5,000 or 26,000 barrels a day: Size of gulf oil spill is a guesstimate

But the new video clips don't clarify one of the biggest unknowns: How much oil are we looking at?

The experts say emphatically that anyone who makes an estimate of the leak by looking at the video is simply arm-waving. There are too many variables. The stuff coming out of the pipe isn't just oil, for example, but a frothing cocktail of oil, gas, brine and sediment from miles below the sea bottom.

BP, however, could try to measure the flow directly with off-the-shelf instruments routinely used in research on deep-sea hydrothermal vents and cold hydrocarbon seeps, according to scientists at the Woods Hole Oceanographic Institution. They said devices that can essentially take a sonogram of the plume could be strapped to one of the robotic submarines that BP has deployed around the damaged well.

"You can use this type of technique to determine the velocity of the particles, and if you know what the area is, it's relatively straightforward mathematics to determine what the volume is," said Andy Bowen, director of the National Deep Submergence Facility at Woods Hole.

BP representatives have spoken extensively with Woods Hole scientists about using scientific instruments to measure the flow. But a BP spokesman, David Nicholas, said the company has decided to focus on stopping the leak rather than measuring it.

"I don't think an estimate of the flow rate would change either the direction or the scale of our response to it," Nicholas said.

That response includes a new option that BP detailed Thursday. Engineers want to thread a second pipe into the end of the pipe that is spewing oil and gas, very much like inserting one drinking straw into the end of another. Ideally the "riser insertion," as the option is called, would divert the oil to a barge on the surface rather than let it pollute the gulf.

BP is also finishing the plumbing on a small dome, nicknamed the "top hat," that could be lowered onto the leak to capture the oil and pipe it to the surface. Other options remain in the mix, none of which have ever been attempted before on a blown-out well in such deep water.

"None of these things are certain. They're the next practical options that have come down our conveyor belt," Nicholas said.

As the oil slick remains largely offshore, the U.S. Army Corps of Engineers is preparing to dredge the Mississippi River to gather sediment for creating an emergency archipelago of barrier islands. On Thursday evening, the Army Corps of Engineers closed a 24-hour comment period in which federal agencies could voice any objections to the massive barrier island restoration plan.

The slick on the surface of the gulf is a moving target for scientists trying to estimate the rate of oil leaking nearly a mile below. It has changed sizes in heavy seas. The oil manifests itself in a variety of forms, which are documented in government reports as silver sheen, transparent sheen, brown oil, tarballs and "orange pancakes or streamers."