U.S. stocks ended August on a weak note, but the decline was not caused by a single disappointing earnings report or one isolated company headline. The market was hit by a broader macro combination: oil above $90 a barrel, a sharp rise in Treasury yields and a renewed belief that the Federal Reserve could raise interest rates in September.
On August 31, the S&P 500 fell 0.33%, the Dow Jones Industrial Average lost 0.70%, and the Nasdaq Composite slipped 0.12%. The losses were modest at the index level, but the cross-asset signals were more important. Brent crude settled around $90.49 a barrel, up roughly 2.7%, while the U.S. 10-year Treasury yield climbed to about 4.77%, its highest level since January 2025.
At the same time, markets raised the implied probability of a September Federal Reserve rate increase to above 65%, up sharply from the roughly one-third probability seen before Kevin Warsh’s Jackson Hole speech.
That combination explains why the session mattered even though the S&P 500 did not fall dramatically. The market is beginning September with a difficult question: Can strong corporate earnings continue to support stocks if inflation risk pushes oil and bond yields higher at the same time?
What Caused Oil Prices to Jump?
The immediate catalyst was another escalation between the United States and Iran. U.S. forces struck Iranian targets on Larak Island in the Strait of Hormuz, and Iran responded with attacks on U.S. military bases in Jordan.
The Strait of Hormuz is one of the world’s most important oil transit routes. Roughly one-fifth of global oil shipments normally move through the area, making any military escalation there more important than a typical geopolitical headline.
Oil prices do not need the strait to be completely closed in order to rise. If insurers increase premiums, tanker operators avoid the region, shipping routes become less efficient or traders believe infrastructure could be targeted, a risk premium can appear quickly.
That is what happened on August 31. Energy stocks benefited, while transportation and consumer-sensitive parts of the market faced a less favorable setup.
Why Did Treasury Yields Rise Too?
Normally, geopolitical risk can push money into U.S. Treasuries and lower yields. This time, investors focused more heavily on inflation.
Higher oil prices can eventually raise transportation costs, airline costs, petrochemical costs and consumer gasoline prices. A short-lived spike may not matter much to the Federal Reserve. A persistent oil shock can.
That is especially important because Fed Chair Kevin Warsh had just used his Jackson Hole speech to say inflation remains too high and that the central bank still has more work to do if underlying inflation does not move clearly toward the 2% target.
The market therefore connected the new oil shock directly to monetary policy. Higher energy prices could make the Fed more cautious about stopping or reversing tightening. That pushed short- and long-term Treasury yields higher rather than lower.
Why Is a 4.77% 10-Year Yield Important for Stocks?
The 10-year Treasury yield matters because it is one of the most important reference rates in global finance. It affects mortgage rates, corporate borrowing, consumer credit, equity valuation models and the return investors can earn from relatively low-risk assets.
When the 10-year yield rises, the discount rate applied to future corporate earnings also rises. That is particularly important for high-growth technology stocks, where much of the expected value comes from profits several years into the future.
A company can still grow rapidly in a high-rate environment. But investors may be less willing to pay an extreme price-to-earnings or price-to-sales multiple for that growth.
That is why rising yields can limit how far AI and software stocks rally even when fundamentals remain strong.
Why Didn’t the Nasdaq Fall More?
The Nasdaq fell only slightly even though bond yields moved higher. That resilience is worth watching.
AI-related earnings expectations remain strong. Nvidia’s latest results reinforced the idea that spending on AI infrastructure is still growing rapidly. Broadcom is scheduled to report next, giving investors another major test of custom AI silicon and networking demand.
As long as earnings estimates continue rising quickly, technology stocks can partially offset the effect of higher rates.
The problem appears if both forces move against investors at once. If AI earnings expectations weaken while Treasury yields remain high, valuation pressure becomes much harder to absorb.
Why Did Energy Stocks Outperform?
Energy was the clearest sector beneficiary.
Higher crude prices improve the revenue outlook for oil producers such as Exxon Mobil, Chevron and ConocoPhillips, assuming production costs do not rise at the same pace.
Oilfield-services companies can also benefit if producers respond to stronger prices by increasing drilling and capital expenditure.
But the relationship is not identical for every energy company. Refiners depend on crack spreads and product margins rather than simply the absolute price of crude. Integrated energy companies also have downstream businesses that can offset part of the upstream benefit.
The main point is that the oil move changed sector leadership on August 31. While the broad market fell, energy became a relative winner.
Which Sectors Are Most Vulnerable to Higher Oil?
Airlines are among the clearest examples because jet fuel is a major operating cost. Cruise operators, trucking companies and logistics firms also face direct fuel exposure.
Consumer-discretionary companies face a second-order effect. When households spend more on gasoline, they have less money available for restaurants, apparel, electronics and entertainment.
This effect tends to be strongest for lower-income consumers. The retail sector is already showing signs of bifurcation, with discount retailers attracting traffic while some discretionary categories remain uneven.
A sustained increase in energy costs could deepen that divide.
How Does the September Fed Decision Fit In?
The Federal Reserve’s September 15–16 meeting is now the central macro catalyst.
Before Jackson Hole, investors needed evidence that another hike was likely. After Warsh’s speech and the oil rally, the burden has shifted. Markets now need evidence that the Fed has a reason not to tighten.
That puts enormous importance on the next two major U.S. data releases.
The August jobs report arrives September 4.
The August CPI report is scheduled for September 11.
If jobs are strong and inflation remains sticky, the case for a rate hike will become stronger. If hiring weakens sharply and inflation cools, the Fed may decide to wait.
Is This a Bearish Signal for September?
Not automatically.
Stocks still finished August with solid monthly gains. The Nasdaq rose more than the other major indexes during the month, while the S&P 500 also ended August higher.
Corporate earnings remain powerful. The market is not entering September from a position of broad fundamental weakness.
The risk is valuation.
Stocks are already pricing a favorable combination of strong earnings and manageable interest rates. If the macro environment becomes less friendly, even strong companies can experience multiple compression.
That does not mean earnings collapse. It means investors pay less for each dollar of expected earnings.
What Should Investors Watch Next?
Five indicators matter most.
First, Brent and WTI crude. If Brent holds above $90 and continues higher, the inflation story becomes more important.
Second, the 10-year Treasury yield. A sustained move above the recent 4.75% area would keep pressure on equity valuations.
Third, the two-year Treasury yield and fed-funds futures. These will show how aggressively markets are pricing the September Fed meeting.
Fourth, the August jobs report on September 4. This is the next major test of whether the economy is slowing enough to change the Fed’s thinking.
Fifth, technology stock resilience. If the Nasdaq can hold up while yields rise, earnings momentum is still dominating. If tech begins to underperform sharply, the rate problem is becoming more serious.
The August 31 selloff was not large enough to call a market break. But it was important because it revealed the new equation for September.
Oil is pushing inflation risk higher. Treasury yields are pushing discount rates higher. And the Federal Reserve is signaling less tolerance for persistent inflation.
The bull market can survive that combination if earnings keep accelerating. If they do not, September could become much more difficult than August.