The prevailing understanding of collusive B2B networks is primarily based on the theories of industrial economists and organizational criminologists. ‘Successful’ collusive industrial networks (such as price-fixing cartels) have been seen to endure due to formal managerial structures of coordination and control. In this paper, we seek to transcend and challenge the understanding of these illegal forms of co-opetition by drawing on evidence from an in-depth examination of four price-fixing cartels that were facilitated chiefly by marketers. Our contribution introduces the notion of ‘shadow networks’ (networks where although attempts are made to ensure secrecy, multilateral modes of network structure dominate akin to ‘normal’ managerial endeavours such as joint ventures) and ‘dark networks’ (networks which appear more opaque and secretive through the adoption of bilateral modes of network structure and limited bureaucracy) to illustrate the types of collusive network forms that may exist. In addition, this allows us to build a deeper understanding of collusive network forms and related inter-firm interaction for an industrial marketing audience. We provide implications for marketing practice, theory, and policy. Specifically, we outline how organizations and the marketing function can perform self-administered antitrust audits in order to help avoid breaches of antitrust. Further, we consider the importance of the two forms of collusive inter-firm networks uncovered where marketers have attempted to render these secret from antitrust agencies, introducing a relatively new line of inquiry to the industrial marketing literature.