The Cross-Hole Seismic Tomography is one step ahead of the conventional Cross-Hole method. Following the same principle than the Cross-Hole technique, in a tomography survey data is acquired simultaneously at different sensors (hydrophones) from seismic waves travelling along multiple raypaths for each shot (instead only one). Combining different shot positions (along the source borehole) and using specialized software, it is possible to transform the traveltime data in 2D maps that reflect the seismic velocity variations between boreholes.