Oil prices are jumping again. How the S&P 500 has performed on days crude has seen big gains may be surprising.

When crude oil prices post sharp single-day gains of 3% or more, the conventional assumption is that equities will struggle. Higher energy costs can pressure corporate margins and consumer spending, and rising oil is often read as a sign of geopolitical stress. Yet historical data on how the S&P 500 has actually behaved on such days suggests the relationship is less straightforward than that intuition implies.

The explanation lies partly in what drives oil higher. When crude rallies on stronger global demand expectations, equities can rise alongside it, since both reflect improving economic activity. Oil-linked sectors within the S&P 500, particularly energy companies, also gain directly from higher crude prices, offsetting weakness elsewhere in the index.

For investors, the takeaway is not that oil and stocks move together reliably, but that the cause of an oil spike matters more than the spike itself. A supply-driven shock carries different implications than a demand-driven one. Watching the catalyst behind crude's move, rather than the headline percentage alone, offers a more useful frame for interpreting equity market reactions.