Abstract: A method of locating a leak in a block of pipes comprises the filling of the pipe with inert gas and the sealing of the pipe. Thereafter, suction is applied to the pipe for drawing air or atmospheric gas into the pipe through the leak. Care is taken to insure that the block of pipes is sealed, except for the suction port and the leak position. Once a layer of air or atmospheric gas is established in the pipe near the leak position, inert gas is drawn from the pipe by the pump, in a direction toward an oxygen or atmospheric gas sensor. By doing this, the layer of air or atmospheric gas is moved along in the pipe from the leak position toward the oxygen sensor. A measurement is taken of the volume of gas being drawn while the layer of air or atmospheric gas is being moved along the pipe. The oxygen or atmospheric sensor indicates when the layer of air or atmospheric gas has arrived.