The Iran and Ukraine wars have exposed the world’s reliance on the Middle East and Russia for diesel Persian Gulf states and Russia have invested tens of billions of dollars in refineries over the past decade to grab a bigger share of the global diesel market. Now, war in both regions has sent exports plunging, squeezing supplies of a fuel that powers much of the global economy. Diesel prices are soaring—they eclipsed $6 a gallon in the U.S. for the first time last week and have kept climbing, hitting $6.45 on Friday. The surge has rattled governments and markets around...