Institutional Equilibrium in Iran’s Banking System: A Graph Model Approach within Game Theory

Introduction: Despite the enactment of Iran’s Interest-Free Banking Law, the implementation of Islamic contracts has largely been reduced to formalism, dominated by low-risk exchange-based contracts. This study combines institutional economics and game theory, employing a graph model to examine behavioral equilibria among key actors and to explore pathways toward more efficient outcomes.

Methods: A mixed-methods design was applied. In the qualitative phase, 26 semi-structured interviews with banking, jurisprudential, and policy experts were conducted and analyzed through three-stage thematic coding. This yielded five main actors (banks, customers, the Central Bank, the Sharia Council, and the government) and 13 behavioral options. In the quantitative phase, priorities were elicited using the Best–Worst Method and modeled in GMCR+. After logical screening, 27 feasible states were generated and evaluated under stability concepts including Nash, metarationality, sequential, limited-move, and future stability. An inverse-game analysis was further employed to identify minimal policy interventions.

Findings: Two stable states were identified, both characterized by formalistic execution of exchange contracts, minimal Central Bank oversight, and flexible stances by the Sharia Council. Unilateral-move analysis showed that banks and customers remain locked in these states due to lower costs, reduced risks, and short-term payoffs, while current intervention capacity is insufficient to break this inefficient equilibrium. Simulation results indicated that a desirable transition requires redesigning institutional rules and reshaping the cost–benefit profiles of actors. Key levers include stringent technology-enabled supervision, economic incentives for genuine participatory contracts, and a coordinated regulatory coalition between the Central Bank and the Sharia Council.

Conclusion: Sustainable reform cannot be achieved through legal or normative adjustments alone. Coordinated policymaking and durable incentive-compatible mechanisms are needed to align micro- and macro-level interests, enabling a more efficient, transparent, and equitable banking system.