Ohio v. American Express Co.  Ohio v. American Express Co., 585 U.S. ___ (2018), was a United States Supreme Court case regarding the nature of antitrust law in relationship to two-sided markets. The case specifically involves policies set by some credit card banks that prevented merchants from steering customers to use cards from other issuers with lower transaction fees, forcing merchants to pay higher transaction fees to the banks. While Visa and MasterCard settled with the United States Department of Justice in 2010, American Express defended its practice by arguing that the anti-steering policies benefited its cardholders, the higher transaction fees helping to maintain member services. While the Department of Justice and several states prevailed during a District Court trial in 2015 citing harm to the merchants, the Appeals Court reversed the District Court's ruling in 2016 by ruling that the plaintiffs had not shown harm to both sides of the two-side market, a novel test in antitrust law. This decision led to some of the states to appeal to the Supreme Court. The case was heard by the Court in February 2018. The Court issued its decision on June 25, 2018, affirming the Appeals Court's ruling that steering provisions do not violate antitrust laws. With this decision upheld, the two-market test could be applied to other venues, particularly to the high tech sector where two-side markets are common. Within the United States, credit card transactions are controlled by four main financial institutions: Visa, MasterCard, American Express, and Discover, making it an oligopoly. Credit cards work as a two-sided market, with the institutions providing benefits to consumers (by allowing them to access lines of credit to make instant purchases) and merchants (by providing them the funds for that purchase instantly). The institutions support this by taking a transaction fee off the merchant's funds, with the fee varying between each institution. Of the four institutions, Discover was the latest offering, created in 1985. To try to compete with the other three institutions on the market, Discover developed a low-cost transaction fee model compared to the other three institutions, which gave incentive for merchants to steer customers towards using Discover cards. To counter this, Visa, MasterCard, and American Express all developed anti-steering contractual language to merchants that prevented them from steering customers into using other cards; this included informing their customers of the different fees and offering discounts and other incentives by using other cards. This also affected the promotion of other cards offered within the institution's network, such as using debit cards with lower fees compared to credit cards.