That’s because the correlation between crude oil and stocks has not been stable over time. For several decades prior to 2000, for example, that correlation was negative, as you can see in the chart below. During those decades, higher oil prices in a given month led to below-average stock-market returns in the subsequent month.

Despite fears about how oil shipments could be affected if Iran targets tanker traffic moving through the Strait of Hormuz, global supply remains strong.

Oil futures declined and U.S. stock indexes rose despite fears Iran will close the Strait of Hormuz, a key waterway for transporting oil around the world.