Abstract: A blowout preventer, particularly for use in drilling bore hole sections near the sea bed, is adapted to prevent blowout of shallow gas in the bore hole. It comprises at least one annular, preferably flexibly expansible and contractible packing element (59, 59'), which by radially directed expansion is adapted to rest sealingly against the wall of the bore hole and close the passage through the annular space of the bore hole. The blowout preventer comprises an inner sleeve element (1) being limited telescopingly displaceable in relation to the outer housing (8) of the blowout preventer and being spring loaded (9) towards extended telescopic position when it is not subjected to extra weight loading, and means which in the relative contracted telescopic position of the sleeve element (1) and outer housing (8) is adapted to close the passage through the inner cavity (48) of the blowout preventer and establish liquid connection to the packing element or elements (59, 59') for inflation thereof.