<p>A method of estimating the position of a subsurface drill bit (10) comprising the steps of a) obtaining seismic data relating to the traveltime between the drill bit (10) and at least two known locations (13) and b) calculating the position of the drill bit (10) relative to a model of the subsurface area, wherein only seismic data obtained in step a) is used to provide information on the drill bit's location. This method does not require magnetic or gyroscopic measurements to be taken. The seismic source/receiver can be associated with either the drill bit (10) or the known locations (13). Hyperbolic approximation or Bayesian Inversion can be used to calculate the drill bit's location.</p>
