Prior to 1970 the Saudi Government faced severe socioeconomic problems two of which were: (1) the contribution of the private sector to the Gross Domestic Product was low, and (2) the oil revenues were the main source of the national income. As the oil revenues rapidly increased between 1972 and 1981, the government used every means at its disposal to encourage the private sector. The goal was to diversify the sources of national income in order to decrease the dependency on oil revenues as the main source of national income. To achieve this the government has provided interest-free loans to the private sector which, along with the demand, has increased the gross domestic fixed capital formation of the private sector. The purpose of this study was to theoretically explain the phenomenal expansion of the private sector. Three models were developed from the least to the most difficult. The main principle of the models is that the expansion of the private sector is stimulated because of the low cost of capital in Saudi Arabia. Since oil revenues (the main source of government expenditures) have decreased in recent years questions have been raised concerning the ability of the private sector to support the economy. It is argued that the demand of national and international markets will increase in the future, thus allowing the private sector to expand further. Even though the cost of capital will increase, Saudi companies will be able to compete either nationally or internationally. In addition, the competitiveness of the Saudi capital market may increase which will, in turn, benefit the Saudi economy.