[en] Tradable emission permit (TEP) systems for greenhouse gases (GHGs) as they could develop following the Kyoto Protocol - that is if they are limited to Annex B countries and are not bound by exchange regulations) - do not appear to be greatly acceptable today, either to the United States or to the European Union. The problem of the uncertainty related to the cost of reducing emissions is strongly highlighted in the United States: in fact, the approach adopted in the Kyoto Protocol, that of quantitative emissions targets, leaves the question of the reduction programme costs wide open. For the European Union, the unregulated TEP system is hardly acceptable because it would not guarantee that the principle of 'supplementarity' adopted in the Kyoto Protocol, that is, the fact that the purchase of permits should be in addition to action taken within each of the Annex B countries. The section two of this paper is an in-depth economic analysis of the european proposal for ''concrete ceilings''. The alternative proposals, formulated in the United States and relating more to permit price ceilings or''trigger price'', are examined in Section 3. After showing that each of the foregoing proposals could have consequences unacceptable to some or others of the parties to the Protocol, Section 4 offers the proposal of a hybrid formula for regulating the rights market. In fact, the main aim of this paper is to show that the implementation of a 'hybrid solution', consisting of limiting the volume of exchanges while at the same time introducing a TEP price ceiling, could provide a market regulation framework effect allowing the benefits of most of the economic advantages to be enjoyed and also having characteristics acceptable to the various parties from an environmental as well as from an international fairness point of view. (A.L.B.)