An assessment of four open ocean boundary stream function conditions based on different data sources for a regional model of the Southeast Pacific Ocean (SEP; 103¿W to the Chilean coast and 16.5¿S to 54¿S) is presented. The model run, with the boundary conditions which most successfully describes the SEP, is forced with a stream function extracted from a global ocean circulation model and is suitable for forming the basis of climate process studies in the SEP. Investigations of other model boundary conditions based on observational data, two using a Sverdrup balance argument to determine the stream function from two commonly used wind stress climatologies and a third using a geostrophic balance argument to determine the stream function from WOCE hydrographic data, were less successful. The main difficulty experienced in all of the model runs was the lack of formation of a sufficiently fresh salinity minimum at intermediate depths. This is linked to the inadequate production of Antarctic Intermediate Water (AAIW) within the model domain or insufficient AAIW propagating across the open boundaries. Comparisons between the model runs highlight the level of uncertainty in aspects of the oceanography of the SEP that govern water mass formation in the region.