The Threshold Effect of Oil Rent on Public Debt in Iran

The abundance of natural resources, as an effective limitation on the government's strategies and the market mechanism, affects the government's behavior from various aspects such as the degree of economic openness, corruption, poverty alleviation, prosperity (Papyrakis & Gerlag, 2007; Segal, 2011) and, as a result, the public debts (Ampfo et al., 2021). Natural resources can raise government capital as a driving force. The growth of government capital can increase the quantity of private capital and production through productivity and cost savings. In addition to encouraging more of these dynamic elements, it can ultimately lead to economic development (Agnor, 2013). Conversely, studies such as Haman et al. (2016) and Arias and Restrepo-Echavarria (2016) show that such a perception is not necessarily correct. The country's reliance on the rent of natural resources can lead to an increase in government spending and a decrease in tax revenue, which ultimately means more public debt. Therefore, the investigation of the factors affecting public debts in developing countries, especially Iran, is of particular importance due to the weakness of the tax system and the existence of a stable budget deficit. In Iran, oil rent is one of the substantial and effective factors in public debts. Understanding the influence of oil rent on public debts enables policymakers and planners to increase the efficiency of government policy while reducing the harmful effects of non-optimal allocation of oil revenues. Considering the importance of the subject, the present research examines the impact of oil resource rent on Iran's public debts.

Investigating the effect of oil rent on public debts was done with the model of Ampfo et al. (2021) and Mamdeli et al. (2021) in which the dependent variable of "ratio of public debts to GDP" is a function of the ratio of "oil rent to GDP", economic growth, and control variables such as inflation, trade openness, and unemployment. The research variables had an annual frequency and were collected in constant 2010 prices. The data source is the World Bank and the International Monetary Fund and covers the period from 1974 to 2021. In order to analyze the effect of oil rent on public debts, the threshold regression approach was used, in which the value of the threshold value, i.e., the ratio of oil revenue to GDP, is calculated by minimizing the sum of the squared errors.

The research model was estimated considering a structural breakpoint and two regimes. The volume of the threshold variable, i.e., the ratio of oil rent to GDP, is 22.23%. The ratio of oil rent to GDP before the threshold is -2.71, and it is -0.644 after crossing the threshold level. In both regimes, oil rent has a negative and significant effect on public debts. In the high oil regime, however, the impact of oil rent on the public debts is less than that in the low oil regime, which is due to the effects of resource curse on the economy. The results of the research on the negative relationship between oil rent and public debt are consistent with the findings of the studies by Sadik-Zada and Gatto (2019), and Mamdeli et al. (2021). Also, Ampfo et al. (2021) and Yang et al. (2023) indicate that oil rents have a negative and significant effect on public debts in the short run. Eskandaripour et al. (2018) show that, with the increase of oil revenues in Iran, the equilibrium level of the government debts is at its lowest level. Therefore, the government can use oil revenues in a favorable way in order to keep down and stabilize the public debts. Economic growth has a non-linear effect on public debt. So, in a low oil regime, economic growth has an increasing and considerable impact on the government debts, but, in a high oil regime, it has a significant and decreasing effect on the public debts. Unemployment rate and trade openness have non-linear effects on public debts; in the low oil regime, they have a decreasing and significant influence on the public debts, but in the high oil regime, they have a positive and significant effect on the government debt. In both oil regimes, inflation has a positive and significant impact on public debts. However, after crossing the threshold level, its intensity decreases.

Conclusions and policy implications: 

The findings show that in Iran's economy, the volume of government debts is decreased with the increase in oil revenues. In a low oil regime, the oil revenues improve the capital and financial resources available to the government by increasing the income, thus providing the ability to adjust the level of the government's debt. In a high oil regime, however, the government needs heavy budget support by adopting ambitious spending policies in various infrastructures and projects. This decreases the effect of oil rent on public debts in the regime of high oil income. Therefore, in the high oil regime, the continued use of oil resource rents may cause a resource curse which not only fails to expand the industries related to oil resources but also suppresses the industries independent of domestic resources and even widespread economic development. As a result, it will create higher challenges for government finances and debts.