The estimation of velocity macro‐models by seismic reflection tomography is studied in three‐dimensions. Inversion techniques based on the kinematics of seismic data require an appropriate parameterization of the geological macro‐model, in particular as far as the velocity field is concerned. The step toward structurally complex geological models is achieved by exploiting a new approach to 3-D depth modeling: GOCAD. The peculiarities inherent to GOCAD triangulated surfaces and its associated discrete smooth interpolator (DSI) have led to the development of original ray‐tracing techniques. By exploiting intensively the topology of the triangulated surfaces, these new algorithms make it possible to reach a good balance between accuracy and computation performance. To build a 3-D macro‐model estimation tool, ray‐tracing is then associated with a least‐squares inversion of depth parameters and velocity parameters from 3-D zero‐offset traveltimes and stacking velocities, or multi‐offset prestack traveltimes from 2-D seismic lines.