The amount of oil spilling into the Gulf of Mexico may be at least 10 times the size of official estimates, according to an exclusive analysis conducted for NPR. At NPR's request, experts examined video that BP released Wednesday. Their findings suggest the BP spill is already far larger than the 1989 Exxon Valdez accident in Alaska, which spilled at least 250,000 barrels of oil. BP has said repeatedly that there is no reliable way to measure the oil spill in the Gulf of Mexico by looking at the oil gushing out of the pipe. But scientists say there are actually many proven techniques for doing just that. Steven Wereley, an associate professor of mechanical engineering at Purdue University, analyzed videotape of the seafloor gusher using a technique called particle image velocimetry. A computer program simply tracks particles and calculates how fast they are moving. Wereley put the BP video of the gusher into his computer. 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. This new, much larger number suggests that capturing - and cleaning up - this oil may be a much bigger challenge than anyone has let on.