More than than 100 contributing scientists worldwide have contributed to Version 6 of the Surface Ocean CO2 Atlas (SOCAT). SOCAT (www.socat.info) is a synthesis activity by international marine carbon scientists with annual public releases. SOCAT version 6 has 23.4 million quality-controlled in situ surface ocean fCO2 (fugacity of carbon dioxide) measurements from 1957 to 2017 for the global oceans and coastal seas, as well as additional calibrated sensor fCO2 measurements.