of 1959 it had received over $100 million of aid from the United States, being the single biggest per capita recipient of American aid. U.S. companies would also play a leading role in the development of the Libyan oil industry. This support was provided on a quid pro quo basis, and in return Libya granted the United States and United Kingdom usage of the Wheelus Air Base and the al-Adem Air Base. This reliance on the Western nations placed Libya at odds with the growing Arab nationalist and Arab socialist sentiment across the Arab world. The Arab nationalist sentiment promoted by Radio Cairo found a particularly receptive audience in Tripolitania. In July 1967, anti-Western riots broke out in Tripoli and Benghazi to protest the West's support of Israel against the Arab states in the Six-Day War. Many oil workers across Libya went on strike in solidarity with the Arab forces fighting Israel. During the 1950s, a number of foreign companies began prospecting for oil in Libya, with the country's government passing the Minerals Law of 1953 and then the Petroleum Law of 1955 to regulate this process. In 1959 oil was discovered in Libya. The 1955 law created conditions that enabled small oil companies to drill alongside larger corporations; each concession had a low entry fee, with rents only increasing significantly after the eighth year of drilling. This created a competitive atmosphere that prevented any one company from becoming crucial to the country's oil operation, although it had the downside of incentivising companies to produce as much oil as possible in as quick a period as possible. Libya's oil fields fuelled rapidly growing demand in Europe, and by 1967 it was supplying a third of the oil entering the West European market. Within a few years, Libya had grown to become the world's fourth largest oil producer. Oil production provided a huge boost to the Libyan economy; whereas the per capita annual income in 1951 had been $25–35, by 1969 it was $2000. By 1961, the oil industry was exerting the greater influence over Libyan politics than any other issue. In 1962, Libya joined the Organization of the Petroleum Exporting Countries (OPEC). In ensuing years the Libyan state furthered its control over the industry, establishing a Ministry of Petroleum Affairs in 1963 and then the Libyan National Oil Company. In 1968 they established the Libyan Petroleum Company (LIPETCO) and announced