To find the residual velocity, two methods can be used. One is to measure the curvatures of the residual moveout. The other is to do many residual migrations and find the velocity that gives maximum stacked energy. The second method is possible because the size of the residual-migration operator is generally much smaller than that of full-migration operator. My future work will include 1) experiments of estimating the curvatures of the residual moveout; 2) dynamic analysis of the residual-migration operator of shot-profile migration; and 3) extension of the results to inhomogeneous media.