In 1944, Campsa's first research center was built in Madrid in association with ENCASO, with the aim of keeping Spain from depending on foreign suppliers and technology. During this period, the research center worked on projects related to shale distillation and fertilizer production, advancing towards the optimization of processes based on the shale oils produced at Puertollano. The center underwent significant expansions and acquired a new testing station for lubricants and fuels, as well as an experimental refinery. Over time the company diversified its activities, making particular headway into the field of petrochemicals.
In 1947, a few years after the end of the war in Europe, the Spanish oil industry witnessed some important changes. The 20-year contract between the state and Campsa came to a close, and the petroleum monopoly was reorganized by law on July 17th, 1947. The old leasing contract was terminated in order to be replaced by a program for the decentralization of services, which simultaneously reinforced the state's intervention in the petroleum monopoly (CAMPSA). The new law established that the state would recover from the petroleum monopoly the ability to award concessions for nearly all hydrocarbon activities, except those related to distribution and commercialization, which remained under the exclusive control of CAMPSA.
In 1948, the company REPESA (Refinería de Petróleos de Escombreras) was established with the purpose of installing a refinery in the Escombreras Valley in Cartagena. Opened in 1951, REPESA's facilities included a lubricants and asphalts production plant, a cogeneration plant, marine facilities at the Port of Escombreras, and a research center. Repsol was REPESA's star brand.
The company Butano S.A. was founded on June 11th, 1957, with the aim to provide door-to-door butane gas delivery. The product stood out for its hassle-free installation, safety, and efficient performance. Comfort had started to fill Spain's homes.
In 1961, the Spanish Ministry of Industry authorized the Marathon Oil Company and PETROLIBER (Compañía Ibérica de Petróleos, S.A.) to form a stock corporation that would construct and operate an oil refinery with an initial annual capacity of 1.2 million tons. In May 1964, CAMPSA collaborated with Chevron and Texaco to drill an appraisal well in Burgos, which would reach production levels of 85 barrels per day.
Hispanoil (La Sociedad Hispánica de Petróleos S.A.) was founded on May 5th, 1965, with the aim of carrying out exploration and production activities beyond Spain. Its first operation was in the Sirte basin in the Libyan desert, one year later.
In 1966, ENCASO (Empresa Nacional Calvo Sotelo de Combustibles Líquidos y Lubricantes) opened the Puertollano refinery in Ciudad Real, the first in inland Spain. Covering 320 hectares, it was connected by an oil pipeline to the Malaga marine terminal.