The transfer performance and power requirements of unconfined sealed end hollow fiber membranes were studied, Membrane modules, operated in the sealed end mode, were pressurized with oxygen and placed within a submerged rectangular jet discharge. This design is especially well suited for use in waters containing high solids concentrations. The membranes have a greater degree of freedom for movement and are, therefore, less likely to become fouled due to solids being lodged within the fiber bundle. Furthermore, because the membranes are not enclosed within a tubular shell, head losses across the membranes are reduced. In a related study, Johnson et al. [1] developed a mass-transfer correlation for unconfined membranes similarly situated within a circular jet discharge. In this study, the mass-transfer correlation developed for circular jets is verified experimentally for larger rectangular module designs better suited for use in large scale applications. The headlosses across the modules are characterized in detail as a function of water flowrate and membrane spacing. These data are used to estimate the power requirements for different designs under a variety of operating conditions. The mass-transfer rates and corresponding power requirements for the unconfined configuration are compared with other membrane configurations.