A field procedure in seismic-reflection studies where, commonly, split-spread and/or cross-spread shooting is used to determine the structural dip of a reflector. The asymmetry of the normal moveout (NMO) associated with a split-spread shot is diagnostic of a dipping reflector, with the up-dip side having the smaller NMO corrections. The true structural dip can be determined from the dip information provided by a cross-spread shot.