The technology of blow-out preventers

If you are curious about the blow-out preventers that are getting the blame for the BP Gulf oil spill, Wikipedia has a short page on their principles of operation:

http://en.wikipedia.org/wiki/Blowout_preventer

Also, M.I.T.'s Technology Review publication has brief article on the topic, followed by dozens of vitriolic reader comments:

http://www.technologyreview.com/energy/25238/page1/