Seismic reflection data calibrated by scientific boreholes have proven the presence of voluminous early Tertiary extrusive volcanic complexes along the northeast Atlantic continental margins. Seismic facies interpretation of representative seismic profiles reveals the presence of one or more characteristic units of seaward-dipping reflectors (SDR) along most margin segments. Other volcanic seismic facies units, including Inner Flows, Lava Delta, Landward Flows, and Outer High are also identified regionally. More than 15 boreholes have sampled the extrusive volcanic complex, recovering subaerial flood basalts, shallow marine hydroclastites, and pillow lavas. Most of the deep holes are drilled into the Landward Flows unit. However, no well-defined reflectors have ever been penetrated within the extrusive complexes. Several of the volcanic facies units have not been drilled at all, including the Inner Flows and the Lava Delta, and only a few shallow holes have been drilled into the SDR. The nature of the intrabasement reflectivity is therefore presently poorly constrained. Representative seismic transects across the conjugate Southeast Greenland-Hatton Bank margins and the Jan Mayen Ridge-More Margin reveal a gross symmetry, as shown by the presence of SDR on all margin segments. In general, however, a lack of symmetry and significant variation in the nature, extent, and volume of the extrusive complexes are apparent. We suggest that the lack of symmetry is largely related to a tectonic control on the emplacement of the lava flows.