A theoretical measure of environmental efficiency.

We study, in a simple model, the partial equilibrium of an industry with n firms endowed by different technologies which have different pollution effects. The price of input (labour) and the demand curve to the industry are given. Pollution is restricted by a tradable market of permits in the industry. We define an environmental efficiency factor for each firm. Given the total dotation of permits, the larger is the environmental efficiency factor, the larger is the firm's contribution to total production. To study the long run efficiency, we explicit the role of capital in production and obtain a proportional environmental efficiency factor. Last, we analyze the consequences of permits' allocations on the profitability of the firms.Environmental efficiency factor, environmental performance, indicators, market of permits, undesirable output.