Bangladesh, Sept. 30 -- The diesel market is already under extraordinary pressure. Refinery disruptions in Russia, the continuing conflict around Iran, constrained shipping through the Strait of Hormuz and depleted inventories have transformed what was once a relatively manageable energy problem into a global economic vulnerability.

Now Washington is considering adding another shock of its own.

President Donald Trump said on September 27 that his administration is “very seriously” considering restricting or banning US diesel exports as American fuel prices surge ahead of the November midterm elections. The statement is not yet a policy decision, but the possibility alone is rattling international energy markets.

The central...