Debates over proposals to liberalise international trade are often heated and acrimonious. They are often argued, in part, on the basis of projections of market conditions after the proposed liberalisation. These argument are often important in influencing trade policy decisions, yet their accuracy is seldom assessed after liberalisation takes place. As a result, the projections may be more influential than they should be. This paper examines the projections of protectionists in the debate surrounding a proposed reciprocity agreement between the United States and British North America over the period 1846-1854 as a case study. The protectionist prophesies on both sides of the border were found not to be supported by the evidence from the subsequent period of reciprocity. A number of reasons for the inaccuracy of the projections are identified.