Irregular spatial sampling complicates antialiasing. 3D seismic surveys are designed to have even sampling in midpoints, but often have irregular sampling in offset. This presents the difficulty that prestack integral operators may have quite different bandwidth along different axes. 3D prestack Kirchoff datuming can be performed in midpoint and offset coordinates, where the data's dip range can be asssumed to be limited relative to its dip range in shot and receiver coordinates. Operator bandwidth can be preserved for a limited range of dips, even when sampling is quite sparse. A midpoint and offset formulation of Kirchoff datuming is more expensive, but may be necessary to make the operator useful for many 3D geometries.