In this paper, we examine a cartel of construction companies’ suppliers of the oil and gas multinational company Petrobras in Brazil. We use an empirical dataset including verifiable court decisions and plea agreements of business executives and companies. This case study offers an account of these corrupt practices in megaprojects and explains how the corrupt cartel, despite being illegal, relied on the self-motivated and mobilized actors that trusted each other. This trust was essential to institutionalize corrupt practices and developing governance rules that were used for over a decade.