A study by the economists Maria Belmira Martins and José Chaves Rosa showed that a total of 244 private enterprises were directly nationalized during the 16 months from 14 March 1975, to 29 July 1976. Nationalization was followed by the consolidation of the several private firms in each industry into state monopolies. As an example, Quimigal, the chemical and fertilizer entity, represented a merger of five firms. Four large companies were integrated to form the national oil company, Petróleos de Portugal (Petrogal). Portucel brought together five pulp and paper companies. The fourteen private electric power enterprises were joined into a single power generation and transmission monopoly, Electricidade de Portugal (EDP). With the nationalization and amalgamation of the three tobacco firms under Tabaqueira, the state gained complete control of this industry. The several breweries and beer distribution companies were integrated into two state firms, Central de Cervejas (Centralcer) and Unicer; and a single state enterprise, Rodoviária, was created by merging the 93 nationalized trucking and bus lines. The 47 cement plants, formerly controlled by the Champalimaud interests, were integrated into Cimentos de Portugal (Cimpor). The government also acquired a dominant position in the export-oriented shipbuilding and ship repair industry. Former private monopolies retained their company designations following nationalization. Included among these were the iron and steel company Siderurgia Nacional, the railway Caminhos de Ferro Portugueses (CP), and the national airline, Transportes Aéreos Portugueses (TAP).