In the presence of lateral velocity variations depth migration rather than time migration should be used to obtain a proper image of the subsurface. If the velocity model is known and if the stack is a good estimate of zero-offset section, post-stack depth migration often gives good results. Normal common-midpoint stacking relays on the assumption of hyperbolic moveout curvature. Prestack depth migration, however, is not dependent on the validity of the common-midpoint assumption, and therefore it should be used in complex areas with strong lateral velocity variations to develope the velocity model and to image the structure properly.