An alternative approach to having a Pigouvian tax is one based on property rights. A practical example of this would be a system of emissions trading, which is essentially a privatization of the atmosphere (Hepburn, 2007). The idea of using property rights in response to an externality was put forward by Coase (1960). Coase's model of social cost assumes a situation of equal bargaining power among participants and equal costs of making the bargain (Toth "et al."., 2001:668). Assigning property rights can be an efficient solution. This is based on the assumption that there are no bargaining/transaction costs involved in buying or selling these property rights, and that buyers and sellers have perfect information available when making their decisions.