imported by 1954. Oil imports by 1955 rose to US$300 million, or over one fourth of total merchandise imports. Perón had made economic nationalism a policy centerpiece. YPF was granted an exemption from steep oil import tariffs levied on private firms, and Article 40 of the Constitution of 1949 stipulated the nationalization of all energy and mineral resources. The deteriorating oil deficit led Perón to court foreign investment in the sector as early as 1947, however, when an oil drilling contract was signed by YPF with U.S. firm Drilexco. Total exploration doubled, and significant reserves in Salta Province were developed. A more controversial joint venture with Standard Oil of California was signed in 1955 for the eventual production of up to 56 million barrels a year. These initiatives were opposed by much of the Army, the opposition UCR, and among others Perón's point man on national oil policy, YPF head Julio Canessa, who was dismissed. The venture ended following Perón's overthrow in September. An erstwhile critic of both the Drilexco and Standard Oil contracts, President Arturo Frondizi enacted policies in 1958 which granted foreign firms rental contracts by YPF over new wells to foster exploration and production. A key part of the developmentalist economic policy advanced by Frondizi, this policy was made with the caveat that oil and gas resources themselves would be renationalized. Thirteen contracts were signed with mainly U.S. firms, whereby each contractor would earn 40% of the revenues produced from the new wells. Private production, which had virtually ceased, grew to become one third of the nation's total. YPF itself benefited by way of a royalty bonanza, which financed record investments. These in turn led a doubling of YPF production to 65 million barrels; including the private sector, Argentina's oil production thus nearly tripled to 98 million barrels by 1962, and despite higher consumption, imports fell to merely one sixth of total demand. These contracts created a controversy referred to by Frondizi himself as the "oil battle," and were ultimately cancelled by President Arturo Illia in 1963 over concerns that YPF would be deprived of adequate returns for its exploration investments; of the foreign firms which had taken part in the 1958 bids, only Amoco remained. The cancellations cost US$50 million in indemnity payments, though they proved fortuitous after the company's discovery of the Puesto Hernández field in 1965. Puesto Hernández, near Rincón de los Sauces, Neuquén