The paper argues that 18th-century merchants were highly dependent on mutualized uses of credit on the one hand, information on the other, and that this mutualization took place mostly outside institutional frameworks. This dependency on personnalized channels of cooperation allowed for the rise of well-organized circles of actors able to erect significant barriers to entry on specific market segments. Two examples of such market-controlling rings are analyzed, using the papers of Abraham Gradis of Bordeaux and Levi Hollingsworth of Philaldelphia. Both traders were able to achieve oligopolistic control of specific market segments, using insider information as a key tool to manipulate prices and transactions, and relying on a ring of allies linked by credit networks and mutual advantage. The paper concludes that standard economic modelling is ill-suited to such a universe of privately created liquidity, segmented markets, and asymmetrical information.