The modalities of negotiation on market access for agricultural and non-agricultural products are an important item of the Doha Development Agenda. The dispersion of tariffs remains very large, translating into sizeable economic distortions. In particular, tariff peaks are numerous and highly protective. This is why the choice of a formula of reduction in tariffs is a sensitive issue. Using the MAcMaps database, we apply various formulas excluding or including peaks at the most detailed level of information on tariffs, considering preferential schemes conceded so far. The resulting changes in tariffs are introduced in a CGE exercise using Mirage. We find that trade and welfare gains are halved when excluding peaks from the negotiations.