The network of Portuguese companies in 1973 has been identified as a relevant element for understanding the economic structure of the country in the decade of 1970–1980. This network had been formed before 1974, during the dictatorship, but it remained after the Carnation Revolution. In spite of such research, this network has not yet been properly analysed, especially through adequate tools from network analysis. This work will detail this network, the different scores of centrality of each company, and their modular structures; it will also discuss estimates from exponential random graph models to identify significant attributes that explain the discovered flows of investment. This work will also detail the processes of vertical integration as well as the specificities of the identified oligopolies.