Oil traders have been given another reason to worry.

Crude prices rebounded more than 1% on Monday after President Donald Trump rejected an Iranian proposal linked to reopening the Strait of Hormuz, reviving fears that the world's most important energy shipping route could remain restricted for longer.

Brent crude futures rose $1.82, or 1.74%, to $106.14 a barrel, while U.S. West Texas Intermediate crude climbed $1.14, or 1.23%, to $93.55 by 2202 GMT, according to Reuters.

The move represents another abrupt shift in a market that has spent recent weeks swinging between hopes for diplomacy and fears of prolonged disruption.

Only recently, traders had been pricing greater optimism around negotiations between Washington and Tehran.

Now the mood has changed again.

Iran had proposed reopening the Strait of Hormuz within a seven-day framework tied to easing military pressure and resuming negotiations. Trump rejected the proposal, saying he wanted a different path toward ending the conflict, while also indicating that negotiations could resume during the week.

For oil markets, the immediate issue is not the wording of the diplomatic exchange.

It is the Strait itself.

Hormuz is one of the most strategically important waterways in the global energy system. A prolonged disruption can affect crude shipments, refined products and natural gas flows across markets far outside the Middle East.

That is why oil prices have become so sensitive to even small changes in the diplomatic outlook.

When investors believe Hormuz could reopen, the geopolitical premium embedded in crude can fall.

When the prospect of reopening becomes less certain, the premium returns.

Monday's rally was a textbook example.

The market had been looking for a signal that diplomatic negotiations might produce a realistic path toward restoring normal shipping.

Instead, the U.S. rejection increased uncertainty.

And uncertainty is expensive in energy markets.

The oil market does not need an actual global shortage before prices rise.

It only needs traders to believe that future supplies could become harder to obtain.

That is particularly important because the conflict has already disrupted a significant portion of normal regional energy flows.

The Strait of Hormuz connects the Persian Gulf with the Gulf of Oman and Arabian Sea, providing a critical route for oil exporters including Saudi Arabia, Iraq, Kuwait, Qatar and the United Arab Emirates.

When that route is threatened, producers and buyers have to search for alternatives.

Some Gulf producers have pipelines that allow them to bypass part of the waterway.

Saudi Arabia, for example, has been relying more heavily on its East-West Pipeline to move crude toward the Red Sea.

But alternative infrastructure has limits.

It cannot necessarily replace the entire volume normally moving through Hormuz.

That is why the market continues to treat the strait as a critical vulnerability.

The latest price rise also highlights how differently Brent and WTI can behave during geopolitical shocks.

Brent is the main international benchmark, and it generally carries a larger premium when global seaborne energy supply is threatened.

WTI reflects U.S. crude conditions more directly.

Monday's settlement prices left the two benchmarks separated by more than $12 a barrel.

That unusually wide spread indicates how heavily international geopolitical risk is influencing Brent.

But the market is not dealing with geopolitical risk alone.

U.S. energy inventories are also important.

Recent data showed U.S. crude inventories increased by 3 million barrels to 426.4 million barrels, surprising analysts who had expected a decline. That increase would normally be a bearish signal because rising inventories suggest supply is exceeding immediate demand. (reuters.com)

Yet crude prices remain elevated.

That tells investors something about the market's priorities.

Geopolitical risk is currently overwhelming some of the traditional supply signals.

A large U.S. inventory build cannot easily offset the potential disruption of a major international shipping corridor.

The refined-products market is adding another complication.

U.S. distillate inventories recently fell by 428,000 barrels to 107.4 million barrels, keeping attention focused on diesel availability. Diesel matters because it is heavily used in trucking, construction, agriculture and industrial activity.

This means an oil shock can spread through the economy in several ways.

Higher crude prices affect refiners.

Higher refined-product prices affect transportation companies.

Higher transportation costs can feed into the cost of moving food and manufactured goods.

Businesses may pass some of those higher expenses to consumers.

And central banks may then face additional inflation pressure.

That connection is becoming particularly important in the United States.

The Federal Reserve is already dealing with a difficult interest-rate environment.

Long-term Treasury yields have climbed to levels not seen in many years, while recent economic data have suggested that U.S. activity remains resilient.

A renewed oil rally adds another potential source of inflation.

That could make it more difficult for policymakers to move toward lower interest rates.

Markets have therefore started treating every major oil-price move as a macroeconomic event.

Monday's rebound is a good example.

The headline was diplomatic.

The reaction was financial.

Oil rose.

Inflation expectations can rise with it.

Bond yields can respond.

The dollar can move.

Equity markets can reprice.

That is why a dispute over a seven-day Hormuz reopening proposal has consequences far beyond the energy sector.

There is also a critical distinction between negotiations and resolution.

Trump's rejection of Iran's proposal does not mean diplomacy has ended.

Reuters reported that Trump expects negotiations to resume this week. Iran has also continued to emphasize diplomacy as a possible route forward, even while maintaining conditions surrounding the reopening of the waterway.

So the market is not necessarily pricing a permanent blockade.

It is pricing uncertainty over how quickly normal shipping can return.

That leaves crude vulnerable to large swings.

A credible ceasefire could push prices lower very quickly.

A new attack or further restrictions on Hormuz could send them sharply higher.

The same is true of Saudi infrastructure.

If Saudi Arabia can continue moving substantial volumes through alternative routes, the market has a greater supply cushion.

If those routes come under attack, the cushion becomes less reliable.

Recent reports of missile threats around Saudi infrastructure have already demonstrated the concern.

That is why traders are watching both diplomacy and physical infrastructure.

The two are now tightly linked.

For consumers, the stakes are obvious.

Oil above $100 a barrel raises the risk of higher gasoline, diesel, transportation and heating costs.

For airlines, shipping companies and manufacturers, fuel is a major operating expense.

For countries that import energy, a sustained oil rally can worsen trade balances and increase inflation.

For oil-producing nations, meanwhile, higher prices can boost export revenue while simultaneously creating new political and economic pressures.

The global consequences are therefore uneven.

The next few days may be particularly important because negotiations are expected to continue.

Markets will be searching for concrete signs that the U.S. and Iran can bridge their differences.

A diplomatic breakthrough could unwind part of the premium that has accumulated in Brent.

But another failure would reinforce the idea that disruptions could persist.

That would keep the market focused on alternative routes, inventories and the possibility of further supply losses.

Monday's move is therefore best understood as a warning from the futures market.

The oil trade has not decided that diplomacy is dead.

It has decided that diplomacy cannot yet be trusted to restore normal energy flows.

As long as Hormuz remains caught in the middle, crude prices can swing violently on every new statement from Washington or Tehran.

Brent at $106 is not simply a reflection of how much oil the world is consuming.

It is a price for uncertainty.

And right now, uncertainty has become one of the world's most expensive commodities.