Round numbers draw a lot of attention in financial markets, but none more so than when oil tops $100 a barrel, a threshold investors have only had to navigate on three sustained occasions over the past three decades.

We could be nearing a fourth, however, as the U.S. war with Iran escalates into the autumn, the sustained invasion of Ukraine by Russia ramps into further attacks on Kyiv, and domestic crude stockpiles slump to the lowest levels since the early 1980s.

And that has big implications for inflation, Federal Reserve interest rate hikes, and the optics of the November midterm elections.

"The round number matters less than what it signals," said Mark Malek, chief investment officer at Siebert Financial. "The market isn't just pricing today's disruption, it's pricing the odds of more disruption to come."

Brent crude futures for September delivery, the global pricing benchmark, topped the $101 a barrel level in Wednesday trading, marking a staggering 40% surge since the start of July.

Brent traded north of $100 briefly in late July, and held north of that level on two multiweek stretches in March and April.

The last sustained hold for Brent over the $100 mark was a three week stretch in March of 2022, shortly after Russia's incursion into Ukraine took crude to $139 a barrel.

The longest stretch of triple-digit prices was seen in the early 2010s, shortly after the global financial crisis, when crude peaked at $122 a barrel in 2012, but traded north of $100 for nearly three and a half years.

We're not there yet, of course, but with oil heading past the $100 mark into September, diesel prices now at an all time high, and no end to either conflict in sight, markets are having to brace for a new reality.

"Somewhere underneath the futures contracts and the probability trackers, there's a much simpler transmission line running straight into a gas station," Malek said, as the AAA reported gasoline topped $4.22 a gallon this week, a 33% increase from last year.

"Energy costs show up fast, and they show up everywhere: heating bills, freight costs, the number on the pump," he added. "It's the kind of price move that doesn't wait for an earnings call to matter to a household budget. It just shows up."

Showing up just 55 days before midterm elections, of course, creates a new and time-sensitive issue for President Donald Trump, who put lower gas and energy prices, as well as tame inflation, at the heart of his reelection campaign.

Those will be hard to demonstrate now that diesel is approaching its own round number, at just a few pennies away from $6 a gallon. At that level, a class 8 long haul truck, the most commonly used freight vehicle in the U.S., will see its overall fuel bill rise by around $30,000 a year compared with early spring.

"Those costs rarely remain with the trucking company," said Ole Hansen, head of commodity strategy at Saxo Bank. "They are passed along through freight rates and ultimately into the price of food, manufactured goods, construction materials and consumer products."

Bond markets are already reacting, pricing in both the prospect of faster inflation and near-term rate hikes from the Federal Reserve, in the form of higher short-term Treasury yields, and counting the cost of longer-term damage to the economy in the form of rising longer-dated yields and added government borrowing costs.

Oil markets, too, are showing a worrying edge to pricing.

Goldman Sachs warned this week that Brent could top $120 a barrel next year if output from the Gulf doesn't improve, and boosted their end of year forecast by $10 to $90 a barrel. Daan ?Struyven, the bank's co-head of global commodities ?research, told Bloomberg TV that "events over the ?last few days do suggest ?that the risk of shipping disruptions broadening and intensifying is an important one."

Current futures markets for long-dated delivery, meanwhile, indicate Brent crude is unlikely to reach pre Iran war levels until March 2029.

Those moves higher, creating an elevated floor for crude and energy prices, are likely to have a blunting impact on stocks as well.

Higher bond yields will hold down gains, rising crude prices will lift inflation readings and slow consumer spending, while the unsettled elements of the current Gulf war will lean on investor sentiment.

The S&P 500, in fact, has gained less than 2% since it first crossed the 7500 point mark on May 14, despite one of the best second quarter earnings seasons on record, renewed faith in the AI investment thesis, and stronger than expected readings for the broader domestic economy.

But it's still within a stone's throw of the all time highs it reached in mid-August, and holding on to an 11.7% gain for the year, a level that Malek at Siebert Financial sees as either "wisdom or complacency." But sometimes both.

"The stock market's resilience should not automatically be interpreted as proof that the danger has passed," he cautioned. "They can simultaneously be rational about long-term fundamentals and complacent about low-probability risks."

We may know soon which one wins over.