This gain was partly offset by a 40% drop in private-sector output, however, such that overall oil production rose by only one-third during the Peronist decade while annual consumption nearly doubled to 70 million barrels. The nation's oil supply thus shifted from 60% domestic in 1945, to 60% 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.