Summary A significant degradation in the quality of Kirchhoff migration images can arise when the migration operator summation trajectory is too steep for a given input seismic trace spacing and frequency content This phenomenon is called “operator aliasing and is strictly distinct from and independent of data aliasing Unfortunately the conditions which lead to significant operator aliasing are common in most 3-D Kirchhoff migration work due to the sparse and irregular nature of 3-D acquisition geometries and the need to minimize the size of 3-D migration input data volumes.