So, here's a fun term you probably hoped to never hear again: stagflation. It's that nasty economic cocktail of stagnant growth and accelerating prices that makes central bankers sweat and investors nervous. And according to longtime market bull Ed Yardeni, it's quietly creeping back into the conversation.

Yardeni, who's been championing a Roaring 2020s bull market for most of this decade, issued a warning on Monday. The current surge in oil prices, he says, could be the catalyst that revives this forgotten risk for the U.S. economy. Historically, the arrival of stagflation has been a reliable precursor to economic recessions and bear markets for the S&P 500 (SPY).

"Spiking oil prices may precipitate a stock market correction rather than a bear market, but the latter is possible," Yardeni said.

The numbers tell a stark story. Since the start of the war in Iran, crude oil has rallied by 45%. Meanwhile, the S&P 500—tracked by the SPDR S&P 500 ETF Trust (SPY)—has fallen by 3%. It's a divergence that has Yardeni recalculating the odds.

Oil Prices Are Reintroducing a Forgotten Risk

Stagflation is the economic equivalent of being stuck between a rock and a hard place. Inflation rises while economic growth slows, leaving central banks with very few good policy options. They can't easily cut rates to stimulate growth without fueling inflation, and they can't aggressively hike rates to fight inflation without crushing growth.

Yardeni still sees the Roaring 2020s as his base-case outlook, giving it a 60% probability for the remainder of the year. But he admits the balance of tail risks around that sunny scenario has shifted noticeably toward darker outcomes. He's cut the probability of a speculative market "meltup" to just 5% while raising the odds of a "meltdown" scenario to 35% for the current year. That's a significant mood shift from a perennial optimist.

The Signal From Oil Prices

Oil shocks have a nasty habit of sending signals that the broader economy hasn't yet received. A sudden spike in energy prices often tightens financial conditions and acts as a brake on growth well before the official economic data starts to show the slowdown.

The most recent example was in 2022, when oil surged after Russia's invasion of Ukraine. The U.S. economy managed to avoid a formal recession, but the stock market didn't get the memo—it still plunged into a bear market. Yardeni thinks today's environment could produce a similar split outcome. His most likely forecast is a 10% to 15% correction in equities rather than a full-blown bear market, though he's careful not to rule out the more severe scenario.

1973 and 1979: The Historic Stagflation Shocks

If you want a template for how this can go wrong, look no further than the 1970s. In October 1973, Arab members of OPEC imposed an oil embargo during the Yom Kippur War. Crude prices roughly quadrupled from about $3 to nearly $12 per barrel. The result wasn't just inflation; it was stagflation—rising prices met a stagnating economy.

Just a few years later, a second shock hit in 1979 after the Iranian Revolution disrupted global oil supply. Prices more than doubled again, pushing an already fragile economy deeper into the stagflation mire and triggering another recession. Those two crises didn't just hurt wallets; they fundamentally reshaped energy and monetary policy for decades. They're the ghost in the machine that economists hope never returns.

Why the U.S. Economy Might Be Better Equipped This Time

Before you start dusting off your bell-bottoms and worrying about a full 1970s rerun, Yardeni points out that the U.S. economy is structurally in a much better place today to withstand an oil shock.

The first reason is something called "energy intensity"—the amount of energy needed to produce a dollar of economic output. This has fallen dramatically. Energy consumption per unit of GDP has dropped about 70% since 1950 and roughly 62% since 1979. We've shifted from a heavy manufacturing economy to one dominated by services, and technology has made everything from cars to factories more efficient.

The second, perhaps more crucial, factor is domestic production. The U.S. is now a net energy exporter. Total U.S. crude output—including natural gas liquids and renewable fuels—stands near 24 million barrels per day, which actually exceeds domestic consumption of roughly 21 million barrels per day. This is a complete reversal from 2007, when the country was importing about 12 million barrels per day.

Think about what that means: an oil shock that once acted as a pure economic tax—sending money overseas and draining consumer spending—now also generates income for American energy companies. It's not a zero-sum game for the domestic economy anymore.

A Market Beginning to Price a Different Decade?

So, where do we go from here? According to Yardeni, the near-term outlook now hinges largely on a narrow strip of water: the Strait of Hormuz, one of the world's most critical oil shipping corridors.

He warns that as long as Iranian drones continue threatening commercial vessels, that route could remain effectively constrained, keeping upward pressure on oil prices. His base case still assumes the Roaring 2020s narrative holds. But the longer the Strait of Hormuz stays disrupted, the greater the risk that markets stop pricing the 2020s and start pricing the 1970s.

Energy shocks have a historical tendency to shift economic regimes faster than investors expect. If oil prices stay elevated long enough for inflation expectations to become unmoored, the entire macro framework supporting the current bull market could begin to change. We could be looking at a shift toward a decade that markets had hoped was permanently in the rearview mirror.

Yardeni's warning is a reminder that in markets, as in life, the past isn't always dead. Sometimes it's not even past.