Fairly large storm-petrel; overall dark blackish-brown with rather narrow white rump band that wraps around the sides. Typical flight style powerful and fairly direct, often with long glides and high, smooth arcs. Pale band on upperwing is typically faint and does not extend to the leading edge of the wing. Uncommon in deep, warm water in the Atlantic and Pacific Oceans; complex and very subtle variation across range. Probably comprises multiple different species. Most similar to Wilson's and Leach's Storm-Petrels, but note squared-off tail (sometimes with a very shallow notch), weaker upperwing bar, long wings, and more direct flight with smooth turns (less jolting than Leach's and less fluttery than Wilson's).