It has been proved that in an homogeneous product industry, price over marginal costs, business stealing, set up costs and free entry imply excess entry from the welfare point of view. The proof assumes identical firms. We show by example that with non-identical firms, those conditions are...

This paper compares the effects of unitary and ad valorem taxes in a homogeneous good market where two technologies are freely available. We find that, both in monopolies and Cournot oligopolies, unit taxes may be welfare superior to ad valorem taxes.