(See Corrections & Amplifications item below.)

The oil well spewing crude into the Gulf of Mexico didn't have a remote-control shut-off switch used in two other major oil-producing nations as last-resort protection against underwater spills.

The lack of the device, called an acoustic switch, could amplify concerns over the environmental impact of offshore drilling after the explosion and sinking of the Deepwater Horizon rig last week.

The accident has led to one of the largest ever oil spills in U.S. water and the loss of 11 lives. On Wednesday federal investigators said the disaster is now releasing 5,000 barrels of oil a day into the Gulf, up from original estimates of 1,000 barrels a day.

U.S. regulators don't mandate use of the remote-control device on offshore rigs, and the Deepwater Horizon, hired by oil giant BP PLC, didn't have one. With the remote control, a crew can attempt to trigger an underwater valve that shuts down the well even if the oil rig itself is damaged or evacuated.