An instant acoustic logging method for use in oil drilling, wherein a drill bit (16) arranged at one end of a drill string (12) and rotated in a well (18) is used as the acoustic source. The method comprises the steps of measuring, at the top (22) of the string (12), the vibration generated therein by the rotating drill bit (16), sensing acoustic signals from the drill bit (16) at at least one point (24, 26) on the ground (28) away from said drill bit (16), and processing the signals to provide data on the rock (32, 34, 36) around the well (18). Said method comprises an additional preliminary step of processing the vibration measured at the top (22) of the string (12) to determine the nature of the pilot signals from the drill bit (16), said data on the rock around the well being obtained by comparing the acoustic signals sensed on the ground (28) with the pilot signals from the drill bit (16).