Abstract: A method and equipment are described for performing measurements while drilling for oil or gas, in particular VSP-measurements employing a seismic source together with sensors such as hydrophones and/or geophones connected to a memory- and calculation device for storing and processing the seismic signals. The seismic source (2) is placed at or in the vicinity of the surface of the earth whereby signals generated by the source are detected by the hydrophones (3,5) or the geophones located in the vicinity of the source (2) at the surface and in the drill string (4). The geophones or the hydrophones (5) in the drill string transmit the detected signals to a memory- and calculation unit (6) in the drill string that processes and transmits the signals completely or partly to a central data processing unit (10) on the rig (7).