Abstract: A blowout preventer assembly for sealing off a well blowout within the confines of the drill stem is disclosed. The blowout preventer assembly comprises an elongated collar member which is located around and is slidable along a section of the drill pipe. Each end of the collar member has an expandable portion made of rubber or the like, which is capable of being expanded to the width of the drill pipe casing. Fixedly attached to the section of drill pipe at a location above the slidable collar member is a rigid metal collar section having around its circumference a plurality of equally-spaced wing flanges tapering down from a right angle at the top of the fixed collar to a slope at the lower end thereof.