A mixture of cornstarch and water best known for entertaining kindergartners could have plugged the spewing Macondo oil well in the Gulf of Mexico, say physicists.

Where regular drilling mud failed to stop the flow, oobleck — a complex fluid that seems to switch between liquid and solid — succeeded in simulations published Jan. 31 in Physical Review Letters.

“We couldn’t do a full scale experiment on a real well that was blowing out 50,000 barrels a day, but to the extent that you can do a smaller experiment in the laboratory it’s basically the same physics,” said physicist Jonathan Katz of...