Cross-well tomography uses the traveltimes of first arrivals to estimate the velocity model between two wells. If the velocity anomalies are large, ray-bending effects must be considered. In this case, one needs to find the trajectories of rays between each pair of sources and receivers. In Figure , I simulate this situation by tracing rays through a smooth slowness model. The rays start from three sources on the left and end to the uniformly spaced receivers on the right. The velocity variations cause the rays to bend accordingly.