A geopolitical flashpoint thousands of kilometres away is rippling through Southeast Asia, exposing a familiar vulnerability: the region’s deep reliance on imported fossil fuels.

Since late February, tensions between the United States and Iran have escalated into open conflict, sending global oil markets into turmoil.

The disruption of the Strait of Hormuz, a vital artery that channels roughly 20 million barrels of oil daily to Asian economies, has tightened supply and driven prices sharply upward.

Across Asean, the effects have been...