Abstract: There is disclosed a blowout preventer used in the drilling and completion of oil and gas wells and having rams which are moved within chambers in a housing which intersect a bore therethrough between positions opening and closing the bore. The zones of the bore above and below the closed rams are respectively connected by first and second passageway means with the outer side of the rams, with one of the passageway means extending through each ram. Each ram is moved by operating means which includes a rod having a lost motion therewith and a packing assembly on its inner end which sealably engages an end surface of the ram which surrounds the opening of the one passageway means to the chamber, as the rod moves inwardly to close the rams, and disengages therefrom, as the rod moves outwardly to open the rams.