Based on our global measurements of CO, taken over 2-8 years at 16 sites, we have estimated the latitudinal and seasonal distributions of the sources. We find that the most concentrated sources of CO, amounting to some 30% of the global production, are in the industrialized regions bounded by 30¿N and 50¿N. About 47% of the CO comes from the whole of the mid-northern latitudes and another 40% comes from the tropics. Our calculations show that the production of CO is significantly higher during spring and summer, particularly in the industrialized middle northern latitudes. From these results it is apparent that the observed seasonal cycle of CO concentrations cannot be explained by the seasonal variation of OH alone. ¿American Geophysical Union 1990