A two-dimensional photochemical model of the atmosphere has been used to calculate regional and global budgets for CH4 and CO in the troposphere. The modeling distributions of these trace gases are compared to relevant observations and show good agreement when the zonal average nature of the model results is taken into account. The chemical and dynamical components of the budgets are investigated and used to explain the seasonal distribution of CH4 and CO in the model. The seasonal variation is governed mainly by the seasonal variation in emissions and transport between the hemispheres. Destruction by OH is also important at certain times of the year. ¿ American Geophysical Union 1993