The situation where a graph of seismic velocity vs. azimuth has an elliptical shape. SH-waves in a transverse isometric medium exhibit elliptical anisotropy. P-or SV-waves, or waves in other symmetry systems, generally do not involve elliptical anisotropy except for special situations. Fitting a hyperbolic NMO equation to CMP data to obtain the stacking velocity of the horizontal component is equivalent to assuming an ellipsoidal wavefront. Nonelliptical wavefronts yield offset-variable stacking velocities. See anisotropy, transverse isotropy, Figure A-14c, and Helbig (1983).