In Philadelphia National Bank (PNB), the Supreme Court held that it is improper to weigh a merger\u27s procompetitive effects in one market against the merger\u27s anticompetitive effects in another. The merger in question, which ostensibly reduced retail competition in the Philadelphia area, could not be justified on the grounds that it increased competition against New York banks and hence perhaps enhanced competition in business banking in the mid-Atlantic region. I will refer to the Supreme Court\u27s prohibition on balancing effects across markets as a market-specificity rule. Under this rule, efficiencies that may counterbalance anticompetitive aspects must be specific to the market in which the anticompetitive aspects are present. ...