How major US stock indexes fared Monday 5/18/2026

Oil prices and stock markets worldwide kept swinging with uncertainty about what will happen with the Iran war. The S&P 500 swiveled between gains and losses in the morning before ending 0.1% lower Monday, its second straight drop since setting an all-time high last week. The Dow Jones Industrial Average added 0.3%, and the Nasdaq composite fell 0.5%.