Abstract: The present invention relates to a method of and apparatus for converting an oil well with natural effluent rise to one with gas-lift of the effluent column, wherein the oil well has a nipple in the production tube provided with a stop-groove and smooth bearing surfaces between which a hydraulic control line comes out. For conversion an inner tube is lowered inside the production tube, the inner tube being provided with a locking system for locking the inner tube to the nipple, and with a safety valve assembly capable of closing both the passage inside the inner tube and the annular passage between the latter and the production tube, under the action of a control fluid supplied by the control line which opens between two seals on the inner tube and which bear against the smooth bearing surfaces when locking is effected.