Large, dark, angular storm-petrel with a deeply notched tail. Looks long-necked and large-billed. Paler brown upperwing band is usually rather faint and does not reach the leading edge of the wing. Typical flight style is smooth and powerful with deep wingbeats. Uncommon from central California to Peru, often in mixed flocks with other species of storm-petrel. Compare with dark-rumped Leach's and Ashy Storm-Petrels, but note flight style, overall shape, and large bill. Also very similar to Markham's Storm-Petrel, which overlaps offshore Middle and South America. Black is bulkier and larger-billed, with a duller upperwing band, and is usually found closer to shore than Markham's.