Scientists are now measuring carbon dioxide in the ocean as part of a coordinated international study of the carbon cycle in the oceans known as the Joint Global Ocean Flux Study (JGOFS). Current plans for JGOFS include a variety of surveys, process studies, and time-series observations. Such an ambitious field program is extremely demanding; the scientific goals require careful and accurate chemical analytical techniques, and the global coverage needs substantial international collaboration. The quality of these measurements is a key concern, as the eventual success of such a survey requires that measurements made at different times, by different investigators from laboratories around the world, be comparable and correct.