The theorem states that if trade in an externality is possible and there are sufficiently low transaction costs, bargaining will lead to a Pareto efficient outcome regardless of the initial allocation of property. In practice, obstacles to bargaining or poorly defined property rights can prevent Coasean bargaining. This 'theorem' is commonly attributed to Nobel Memorial Prize in Economic Sciences winner Ronald Coase during his tenure at the London School of Economics, SUNY at Buffalo, University of Virginia, and University of Chicago.