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.

Global equity markets advanced on Monday while oil prices settled sharply lower after hitting multi-month highs, as markets shrugged off the effects of the escalating Middle East conflict, with Iran firing retaliatory airstrikes against U.