An investigation of sediments from ODP Site 959 in the Eastern Equatorial Atlantic has been conducted in order to determine whether reducing continental margin sediments, variably influenced by coastal upwelling and restricted bottom water circulation, could be used to reconstruct past variations in the Os isotopic composition of seawater. The results of this study show that Re concentrations (5 to 90 ppb) are pervasively enriched relative to the estimated average crustal Re concentration of 0.5 ppb. As a result of these large Re enrichments, significant in situ production of 187Os by 187Re decay has occurred subsequent to sediment deposition. Initial 187Os/186Os ratios can be calculated from biostratigraphic ages and measured 187Os/186Os and 187Re/186Os ratios. These calculated initial ratios correspond closely to the seawater Os isotope evolution curve. This finding is significant for two reasons. First, it provides evidence that variations in the Os isotopic composition of the Pacific and Atlantic ocean basin have been very similar during the Cenozoic. Second, it suggests that coeval suites of reducing continental margin sediments can be used to construct whole rock isochrons with initial 187Os/186Os ratios indicative of the Os isotopic composition of seawater at the time of sediment deposition. Implicit in this approach are the assumptions that the majority of Os in these samples is scavenged from seawater at the time of sediment deposition, and that subsequently the system has remained closed with respect to both Re and Os.