This preliminary study presents a new method for the determination of dissolved gases in sea-water. After headspace extraction, gaseous compounds are separated by GC on a dual column adsorption system, The individual species are thereafter eluted to three different detectors (thermal conductivity, flame ionization and FPD) using a second switching valve, The analysis is quantitative for methane and carbon dioxide with limits of determination of 0.1 and 50 mu mol l(-1), respectively, and corresponding standard deviations of 4 and 7%, and has been applied to deep sea hydrothermal samples, Further optimization is necessary to allow the quantitative determination of hydrogen sulfide, nitrogen, oxygen and carbon monoxide.