On December 3, trade ministers from members of the World Trade Organization (WTO) will begin three days of meetings in Bali, Indonesia. Trade Facilitation, estimated to add $1 trillion to global income, features prominently in the negotiation agenda. However, official estimates depend on too many unjustifiable assumptions. Inaccuracy accumulates in several stages of the estimation process: in estimating the gains from trade facilitation for a sample of countries, in scaling up the gains to the global level and in estimating employment gains. This brief describes the estimation procedure and shows that the resulting figures are too uncertain to underpin any policy decisions.