Market mechanisms are increasingly being considered as a tool for allocating somewhat scarce but unpriced rights and resources, such as air and water. Tradable permits have emerged as the most cost--effective measure leading to the emergence of both nationwide (SO2) and supranational (CO2) emission permits markets. By means of the dynamic optimization of companies which are covered by such environmental regulations, it develop an endogenous model for the emission permit spot price dynamics that account also for the presence of asymmetric information.