The relationship between primary production in the surface ocean and export of particulate organic carbon (POC) on sinking particles is examined in studies that have utilized 234Th as a tracer of upper ocean export. Comparisons between production and export are made in a wide range of open ocean settings and seasons. The results indicate that much of the ocean is characterized by low POC export relative to primary production (export/production=ThE<5--10%). Exceptions to this pattern are found during blooms at high latitudes, accompanying spring blooms at midlatitudes, and perhaps in association with more episodic export pulses. These sites of high export are most often characterized by food webs dominated by large phytoplankton, in particular diatoms. These results can be used to better parameterize surface export in biogeochemical models in order to provide a more accurate prediction of the flow of C and associated nutrients in the oceans. ¿ 1998 American Geophysical Union