The results of two simple multilevel numerical experiments for the deep ocean circulation are decomposed into vertical modes, and a comparison is made between the decomposed flow fields and the results of corresponding reduced-gravity models. Although the basic equations of the multilevel model are fully nonlinear, it is a good approximation that first-mode flow fields of the multilevel model are the linear responses of a reduced-gravity model to a concentrated source and an almost uniformly distributed sink. In the multilevel model forced by a surface differential cooling the vertical advection of density anomaly in the region where the cooling is strongest acts as the major mass source for the first baroclinic mode. The convective adjustment, on the other hand, has only a minor contribution to the source for lower modes. The interior broad, uniform sink for the first mode, which is an important element in the Stommel-Arons model, is provided by the vertical diffusion of the basic density stratification. For such high modes as to constitute the stacked jets along the equator, nonlinear forcing at lower latitudes cannot be neglected. ¿ American Geophysical Union 1995