Argo is an observation system for the Earth’s oceans that provides real-time data for use in climate, weather, oceanographic and fisheries research. Argo consists of a large collection of small, drifting oceanic robotic probes deployed worldwide. The probes measure the salinity and temperature of the ocean at depths down to 2 km. Once every 10 days, the probes surface to transmit the measurements to scientists on shore via satellite. The data collected are freely available to everyone, without restrictions. The initial project goal was to deploy 3,000 probes, completed in November 2007. The Argo program is a collaboration between 50 research and operational agencies from 26 countries, with the United States contributing over half the total funding (as of December 2004). Argo is a component of the Integrated Ocean Observing System.