The results of the two models suggest that governments of developing countries producing at least eight primary products -coffee, cocoa, tea, bananas, bauxite, copper, tin and tropical timber (not used in the modified model) - could benefit by simultaneously levying a tax on the export of the product concerned. In the case of cotton, palm oil, rubber and sugar, the optimal rate seems to be low, while five others - phosphate rock, iron ore, manganese ore, nickel and zinc - are not suitable for such an arrangement.