The South Pars Gas Field, recognized as the world’s largest natural gas reserve and a shared endowment between Iran and Qatar, represents a paradigmatic intersection of energy geopolitics and transboundary resource governance. Employing qualitative document-based content analysis and a case study approach, this research addresses the central question of how technical, economic, and political challenges shape joint exploitation patterns and bilateral relations. The working hypothesis posits that the absence of a comprehensive joint legal regime, coupled with external pressures, has rendered competitive dynamics more dominant than cooperative arrangements. The findings indicate that reservoir pressure decline, gas flow migration toward the Qatari sector, sanctions-induced developmental delays on the Iranian side, and Qatar’s extensive expansion of the North Dome Gas Field have not only diminished Iran’s relative share but also altered the geopolitical balance in the Persian Gulf. Interpreted through the theoretical lenses of energy geopolitics and complex interdependence, this situation reveals a dual structure characterized by negative competition alongside latent potential for positive cooperation. The study underscores the need to strengthen energy diplomacy, formulate a joint resource management agreement, and prioritize pressure-enhancement technologies within Iran’s policy agenda to reinforce national energy security and promote regional stability.