Several morphological and functional characteristics that affect the jet propulsion of salps are described, based on observations of living animals in situ and in the laboratory. A velocity profile of water flowing through the salp and its feeding net is determined from video frames, and velocities of the jet efflux are related to forward movement of the animal. Analysis of the size and spacing of vortices in the jet trail indicates that the theoretical augmentation of thrust from a pulsed jet may indeed affect the locomotory efficiency of salps. The external morphology of several species of solitary-generation salps indicates selection for streamlining in most, and the architecture of the chains of aggregate-generation individuals has a significant effect on their locomotory capability. Calculated costs of locomotion for several salp species are lower than for all other jet-propelled organisms. Differing locomotory capabilities and their consequences may be one of the main characteristics that isolate species of salps.