A blowout preventer and flow regulator, comprising blocks, each having a channel and plates to close it. The blocks are placed over a pipe through which oil or other fluid is escaping, so that the pipe is in their channels. Alongside the channel in each block are one or more plates, having diameters somewhat larger than the diameter of the channel. One or more pistons are attached to each of the plates. Explosive charges, or other suitable means, move the pistons to propel the plates across the channel to seal it off and stop the leak. Flanges may limit the pistons' movement. Gears can engage teeth on the pistons to withdraw the plates from the channel, to reopen it and allow the flow of oil or other fluid to resume. Plates may be withdrawn part way from the channel, to reduce and control the flow, without cutting it off completely.