A video released by BP this week has underscored questions about the rate at which oil is spewing from a broken pipe on the Gulf of Mexico seabed.

BP and government officials have pegged the leak resulting from the Deepwater Horizon rig disaster at 5,000 barrels a day, or about 200,000 gallons. But a scientist who analyzed the video of the gushing pipe said Thursday the oil flow appeared to be much greater.

“I spent a couple of hours this afternoon analyzing the video, and the number I get is 70,000 barrels a day coming out of that pipe,” said Steve Wereley, a Purdue University mechanical engineering professor.

Wereley, who has written a book on flow measurement, said his figure was an estimate that could be off by plus or minus 20%.

“BP has said you can’t measure this. I agree you can’t measure [the flow] to a very high degree of precision,” he added. “But that doesn’t mean you can’t get a good estimate. This estimate, I think, is much better than the 5,000 barrels a day they have previously been floating.”

In response to Wereley’s estimate, Rep. Edward J. Markey (D-Mass.) said late Thursday that he would launch a formal inquiry into the matter.

“I am concerned that an underestimation of the oil spill’s flow may be impeding the ability to solve the leak and handle the management of the disaster,” said Markey, a member of the House Energy and Commerce Committee.

Wereley arrived at the number by comparing individual frames of the video and tracking how fast a swirl of spewing oil moved from one frame to another. He then calculated the flow based on the size of the pipe.

He conducted the exercise after National Public Radio called him and asked whether the flow could be measured. The network reported Wereley’s results Thursday.

BP spokeswoman Rebecca Bernhard said the company is standing by the 5,000-barrel figure. “We look at the fact that it’s coming out of the riser [pipe] in several ways. We look at it from satellite imagery, overflight observations and on-the-water observations.”

She said none of the methods were exact. “We said that from the beginning.”

Last week BP officials told members of Congress in closed-door briefings that the spill could amount to 60,000 barrels a day in a worst-case scenario.

bettina.boxall@latimes.com