During September--October 1991 over 500 determinations of carbonyl sulfide (OCS) were made in the troposphere over the North Pacific Ocean as part of the NASA Pacific Exploratory Mission-West A project. Three distinct regimes were found in the distribution of OCS in the Pacific troposphere during this period. Under conditions of remote Pacific marine air, OCS had a mean of 495 parts per trillion by volume (pptv) with a standard error of the mean of 0.6 pptv and a standard deviation of 8.8 pptv. Under conditions of air transported from Asia and the North American Arctic, both elevated and depleted levels of OCS were found. Decreases in OCS of 10--20% from the remote Pacific mean were highly correlated with decreased carbon dioxide levels. Increases of 10--20% of OCS were highly correlated with increased carbon disulfide and other chemical indicators of anthropogenic sources. The constancy of the OCS mean for the remote Pacific marine air masses can be used to better understand the budget for OCS and its impact as a source of stratospheric sulfur dioxide. ¿ American Geophysical Union 1996