Carbonyl sulfide (OCS) in the boundary layer of the marine atmosphere was measured by gas chromatography with flame photometric detection on board ship following a meridional transect in the Atlantic Ocean between 37 ¿S and 51 ¿N. Overall, OCS levels from 174 individual samples averaged 537 ppt with a standard deviation of 104 ppt. A pronounced northward increase in OCS of, on the average, 26 ppt per 10¿ latitude was found, together with a mean interhemispheric ratio of 1.25 between OCS in northern and southern hemisphere air masses. OCS correlated significantly with CH4 and CO values obtained during the cruise by an independent investigator. ¿ American Geophysical Union 1990