Diesel prices remained elevated on Wednesday as tighter refined-product supplies kept pressure on fuel markets in the United States and Europe. U.S. ultra-low sulfur diesel futures jumped 7.4% on Monday to settle at $4.19 a gallon. That marked the contract’s biggest daily gain since July 13. Early Wednesday trading put the contract near $4.28 a gallon, while European diesel refining margins remained at historically high levels after rising nearly 10% on Monday.