Which mechanism determines the planetary atmospheric inventories of various gases is an important problem. It has been suggested that Venus' atmospheric CO2 abundance is controlled or buffered by carbonation reaction on the surface (carbonate buffer). According to this hypothesis, the formation or decomposition of carbonate stabilizes atmospheric CO2 concentration. However, the amount of carbonate existing on the Venus' surface is not established yet. Using a stability analysis that combines the greenhouse effect, carbonation reaction, and topography, we place an upper limit to carbonate on Venus. This upper limit of carbonate is only about 4 bar of CO2 and is much smaller than the amount of CO2 in the atmosphere. This suggests that the present CO2 concentration in Venus' atmosphere is not controlled by the carbonation reaction but by the total abundance of CO2 in near surface layers.¿ 1997 American Geophysical Union