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Welcome to Thoughts on the Market. I'm Serena Tang, Morgan Stanley's chief cross asset strategist. Today, what happens if your main diversification strategy suddenly stops working because of oil price moves? It's Tuesday, March 10th at 10:00am in New York. For decades, investors have relied on the idea that stocks and bonds return tend to move in opposite directions. When equities fall, bond prices often rise, helping cushion portfolio losses. But that relationship isn't guaranteed. Between 2021 and 2023, coming out of a pandemic, stocks and bonds sold off together, and the traditional 60:40 equity bond portfolio suffered its worst annual performance in nearly a century. Now, recent geopolitical tensions and rising oil prices are raising a familiar concern for investors. Could that uncertainty dynamic return? At first glance, oil prices may seem like a narrow commodity story, but in reality they can shape the entire macroeconomic environment. The classic negative correlation between stocks and bonds depends on a fairly simple economic pattern growth and inflation moving in the same direction. When economic growth accelerates, inflation often rises as well. In that environment, equities may perform well while bonds weaken. But when growth and inflation move in opposite directions, the relationship between stocks and bonds can flip. That's what happened coming out of the pandemic. Bond investors were worried about rising inflation, while equity investors were worried about slowing growth. In that scenario, both asset classes returns declined at the same time. A sustained oil price shock could potentially recreate those conditions. Higher oil prices can push up inflation while also weighing on economic activity, a combination that economists often refer to as stagflation. If markets begin to price in that kind of environment again, the relationship between stocks and bonds could could shift back towards that less favorable regime. Despite recent volatility tied to tensions in the Middle east, the relationship between stocks and bonds today still largely reflects the traditional pattern. Overall stock bond returns correlation remain negative, meaning bonds can still help diversify equity risk. In fact, correlations between US stocks and two year treasury returns have been trending negative since 2024 and a longer term basis they are now extremely negative relative to the past three years. But the key point here is that not all bonds behave the same way. Many investors think of government bonds as a single asset class, but the maturity of the bond how long it takes to repay matters a lot for diversification. Shorter dated bonds such as two year US Treasuries have maintained stronger negative correlations with equities. Longer dated bonds, however, particularly the 30 year treasury, have behaved a bit differently. The correlation with stocks has been stickier and less negative, partly because markets increasingly view longer dated bonds as risky. As a result, the difference between how 2 year and 30 year treasuries move relative to stocks has remained unusually wide for several years. In recent days, oil prices have been rising, linked in part to the concerns around the Strait of Hormuz. That's pushing up yields at the front end of the treasury curve, creating what's known as bear flattening. In other words, short term interest rates are rising faster than long term ones, reflecting markets placing more emphasis on inflation risks. And that brings us to the key questions for investors. Which risks will dominate from here? Is it going to be higher inflation or slower growth? The answer could determine which assets provide better diversifications in the months ahead. So the takeaway is this Higher oil prices and geopolitical risks could increase the chances that stocks and bonds move together again. But diversification isn't disappearing, it's just becoming more nuanced. For investors, the real question isn't whether bonds diversify portfolios, it's which bonds do. Thanks for listening. If you enjoy the show, please leave us A review wherever you listen and share your thoughts on the market with a friend or colleague today.
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Podcast: Thoughts on the Market
Host: Serena Tang, Chief Cross Asset Strategist, Morgan Stanley
Date: March 10, 2026
Duration: ~5 minutes
This episode explores whether a traditional diversification strategy—relying on the negative correlation between stocks and bonds—remains effective amid rising oil prices and renewed geopolitical tensions. Host Serena Tang examines how recent events, especially volatility in oil markets, could reshape portfolio risk management and asset allocation decisions, with an emphasis on the nuances of bond types in maintaining effective diversification.
For decades, investors assumed stocks and bonds move in opposite directions, buffering portfolios from large losses.
Quote:
“When equities fall, bond prices often rise, helping cushion portfolio losses. But that relationship isn't guaranteed.”
—Serena Tang [00:28]
This relationship broke down between 2021–2023, as both stocks and bonds fell during the post-pandemic period, delivering the worst 60:40 portfolio performance "in nearly a century."
Rising oil prices are not just a "narrow commodity story," but shape the broader economic and market landscape.
The traditional negative stock-bond correlation depends on growth and inflation moving in tandem—both rising or both falling.
Quote:
“The classic negative correlation between stocks and bonds depends on a fairly simple economic pattern: growth and inflation moving in the same direction.”
—Serena Tang [01:14]
When growth slows and inflation rises (as with stagflation), stocks and bonds can both move downward together.
Events like an oil price shock can trigger such a scenario, threatening portfolio diversification strategies.
“Correlations between US stocks and two-year treasury returns have been trending negative since 2024...”
—Serena Tang [02:40]
The nuances of bond maturities are critical:
The spread in correlation behavior between these types is “unusually wide for several years.”
Quote:
“Many investors think of government bonds as a single asset class, but the maturity of the bond—how long it takes to repay—matters a lot for diversification.”
—Serena Tang [02:56]
Recent geopolitical tensions in the Middle East, particularly around the Strait of Hormuz, have spiked oil prices.
This scenario increases short-term Treasury yields faster than long-term yields—a pattern called “bear flattening.”
Quote:
“In recent days, oil prices have been rising, linked in part to the concerns around the Strait of Hormuz. That's pushing up yields at the front end of the treasury curve, creating what's known as bear flattening.”
—Serena Tang [03:43]
Will higher inflation or slower growth be the dominant market risk?
Main takeaway: Diversification remains important, but a more nuanced approach is needed—particularly in selecting among bonds.
Quote (Key Takeaway):
“Higher oil prices and geopolitical risks could increase the chances that stocks and bonds move together again. But diversification isn't disappearing, it's just becoming more nuanced.”
—Serena Tang [04:34]
On Portfolio Strategy Breakdown:
“Stocks and bonds sold off together...the traditional 60:40 equity bond portfolio suffered its worst annual performance in nearly a century.”
—Serena Tang [00:49]
On Stagflation Risk:
“Higher oil prices can push up inflation while also weighing on economic activity, a combination that economists often refer to as stagflation.”
—Serena Tang [01:50]
On the Need for Nuanced Diversification:
“The real question isn't whether bonds diversify portfolios, it's which bonds do.”
—Serena Tang [04:57]
Rising oil prices—driven by new geopolitical risks—may challenge the traditional negative correlation between stocks and bonds, threatening classic diversification strategies. While bonds can still serve as a hedge, investors need to understand the nuances between bond maturities. Short-term Treasuries continue to offer diversification benefits, while long-dated bonds act less predictably. The path forward will depend on whether markets focus on inflation or growth risks—making thoughtful, nuanced portfolio construction all the more critical.