Can you shut off an oil well by squeezing a pipe shut?

Can you shut off an oil well by squeezing a pipe shut?
Yes, an oil well can be "shut off" by the use of a device that has a hydraulic ram that can crush and seal a pipe (or simply shut a valve) to secure a wellhead. The so-called "blowout preventer" is such a device, but in the case of the current disaster in the Gulf of Mexico, the device failed (owing to a failure to replace a battery, as one report had it).