Ideas about key factors in the oceanic mass balance of dissolved, reactive phosphate have changed substantially. I present an integrated overview of these here, with an emphasis on evaluating the burial sinks for P and defining areas needing further research. The major source of reactive P to the ocean is river input. Reactive P is delivered to the oceanic sediment-water interface primarily in particulate organic matter. P scavenged by hydrothermal iron-rich oxyhydroxide particles, with uptake in proportion to deep water phosphate concentrations, represents a substantially smaller flux to the sediment-water interface. Diagenetic transformations are important influences on the form of reactive P burial in marine sediments. P burial occurs with organic carbon burial and as P associated with iron-rich oxyhydroxide particles and coatings. Formation of authigenic P-rich phases, presumably apatite, at the expense of organic P and oxide-associated P, is significant in open ocean marine sediments. The authigenic P sink may represent a substantially larger portion of the sedimentary burial than indicated by previous estimates focused on P burial in organic-rich continental margin sediments. ¿ 1998 American Geophysical Union