The optimal path of energy and CO2 taxes for intertemporal resource allocation The purpose of this paper is to extend the dynamic resource allocation problem by including stock externalities like accumulated CO2 and SO2 emissions as well as flow externalities like waste of energy or pollutants which can be abated (SO2). The objective is to examine how the evolution of enegy CO2 tax rates can adress these problemes in an optimal way. The concern about the time profile of an energy tax arises from the fact that fosil fuels are an exhaustible resource and that global warming being an consequence of carbon accumulation in the atmosphere is a stock externality problem. We use a micro model of a firm which maximice profits uses energy as one of its inputs and is confronted with a varying energy tax. It reacts by substitution by changing its output level by investing in energy efficient technology or by purchasing abatement equipment. The government is well aware about firms reaction on price signals. It maximizes a steam of social welfare by choosing an optimal path of its instrument an energy tax. Our analyses supports the idea of a first rising and later falling tax over time.