Ships are anchored off the coast of Khasab in Oman's Musandam Governorate, near the Strait of Hormuz, on October 2, 2026. (Photo by AFP via Getty Images)

Oil prices were surging on Thursday, as a tanker was struck north of Qatar as a report said the Trump administration was thinking about resuming war against Iran ahead of the midterm elections in November.

That sent the lead Brent crude oil contract (BRN00) up by about 4%, to $104.14 per barrel, as the West Texas Intermediate contract (CL00) rose by a similar percentage to $91.84.

MarketWatch looked at isolating just the days when oil prices rose a lot to see its effect on stocks.

Using FactSet data, there were 42 days when Brent crude prices rose at least 3% in a single session this year. There is nothing magical about 3%, but it's high enough to warrant attention from traders.

The S&P 500 SPX fell during exactly half of those episodes - 21 times in all. And the average move for the S&P 500 on those days was positive - though just barely, at 0.03%. The median move was also positive, again just barely, at 0.01%.

The correlation between stock prices and oil was negative - meaning, when one goes up, the other goes down - at -0.37 on a -1 to +1 scale.

Granted, it's looking on day 43 of a big up for crude that the S&P 500 will decline, as S&P 500 futures (ES00) were down 0.4%.

-Steve Goldstein