When I started working on this article, the national average price for diesel was about $6.43 a gallon. That number is already wrong.

The U.S. Energy Information Administration put the September 21 average at $6.53. On the West Coast, it was $7.46. In California, $8.25. Normally, having a number go stale before you finish an article is annoying. This time, it is the article.

School buses have been running for several weeks. The first serious fuel invoices of the 2026-27 school year are arriving. Transportation directors who built budgets around something resembling normal diesel prices are beginning to see what happens when the fuel line stops behaving like a line item and starts behaving like an event.

And nobody running a school transportation department gets to solve that problem by driving fewer children to school.

A family might cancel a road trip. A transportation director still has 83 routes leaving tomorrow morning.

The buses run. The question is what they run on.

This Was Supposed to Be the Spike

The strange part about $6.53 diesel is that we already had the crisis.

The spring price spike sent transportation departments back to their budgets and crude oil above $100 a barrel. The International Energy Agency called the Middle East conflict and near shutdown of tanker traffic through the Strait of Hormuz the largest oil supply disruption in the history of the global market.

Before the conflict, roughly 20 million barrels of crude oil and petroleum products moved through the Strait each day, about one-fifth of global oil consumption. For a period, those flows slowed to a trickle.

Diesel was especially exposed.

The September 21 national average is now nearly $2.80 higher than a year ago. California diesel is more than $3.25 higher. For a fleet buying thousands of gallons, the decimal points get expensive quickly.

And dependence on one fuel starts looking different when that fuel won't behave.

Propane Doesn't Have to Be Wonderful. Diesel Has to Be Expensive.

Propane advocates have spent years making their case around fuel cost, emissions, maintenance, and domestic supply. Think back to how many years you’ve seen those city-owned Ford pickups and sedans driving around proudly displaying the propane logos.

Some arguments are stronger than others, though. And at today's diesel prices, the fuel-cost argument doesn't need much decoration.

More than 24,000 propane school buses now serve roughly 1,100 school districts across 49 states, according to the Propane Education & Research Council. School Bus Fleet's own 2026 contractor survey found propane in use among 53% of responding fleets. Thirty-six percent included propane among the fuels planned for future purchases.

Propane usage is no longer a science project behind a maintenance garage.

Bonny Eagle School District in Maine, for example, has reported saving more than $75,000 with propane compared with diesel. The district operates 30 propane buses and installed a 17,000-gallon on-site tank.

And, oh wait, one more thing. Bonny Eagle reported roughly 9 miles per gallon from diesel compared with 4 to 5 from propane.

And propane still saved money. That's why pump-price comparisons only get you so far. A transportation department doesn't operate gallons. It operates miles.

Fuel cost per mile matters. Then maintenance, infrastructure, acquisition cost, uptime, and vehicle life enter the conversation.

Of course, propane doesn't automatically win that calculation. You need to run your specific numbers. But $6.53 diesel gives it a considerable head start.

Propane Didn't Get Diplomatic Immunity

There is a tempting argument that propane escaped the diesel spike because U.S. propane supply is heavily domestic. That's only partly true.

The United States benefits from substantial domestic propane production, much of it associated with natural gas processing and refining. That gives American propane fleets a different supply profile from diesel.

But propane isn't living on another planet. The same global disruption that drove crude and diesel higher also affected liquefied petroleum gas moving through the Middle East. The IEA identified LPG among the products experiencing higher prices following the Hormuz disruption.

This isn't an easy-to-write story about one fuel being exposed to geopolitics while another somehow obtained diplomatic immunity. It’s just a story about degrees of exposure.

Keep an Eye on EPA, Not a Hand on the Money

We’ve written a bit about how the EPA canceled the 2024 Clean School Bus rebate round earlier this year and announced plans to revamp the program for a new 2026 grant opportunity.

What you may not remember is that the agency has also asked for input on broader fuel choices. As of late September, however, the final Notice of Funding Opportunity and its eligibility requirements have not been published.

So don't spend all the grant money yet.

What we know is that EPA says more information is coming later in 2026 and that it wants the revamped program to give districts greater fuel choice.

For fleets planning replacements, that's worth watching. Until the actual funding rules arrive, though, the economics still need to work without imaginary federal dollars.

Diesel Isn't Going Away

There is another number in School Bus Fleet's contractor survey worth mentioning.

Ninety-five percent of responding fleets still use diesel. Even now, 71% listed diesel among fuels planned for future purchases.

I’m sincerely aware that transportation departments don't replace fleets because somebody wrote an article about fuel prices.

The reason is that diesel has decades of infrastructure behind it. Technicians know it. Drivers know it. Fueling networks exist. Parts and service networks exist. Fleets understand how these buses behave after five, 10, 15 years.

Those things have economic value too.

Propane requires fueling infrastructure and technician familiarity. Electric brings even more infrastructure issues, charging, electrical capacity, route length, climate and acquisition cost into the calculation. Gasoline is getting another look as well.

There is no universal answer hiding in those numbers. There is, however, a pretty good argument against assuming tomorrow should look exactly like yesterday.

The Question Isn't Which Fuel Wins

Fuel debates have an unfortunate habit of turning into football games where you quickly pick a side. Diesel. Propane. Electric. Gasoline. CNG.

Then, people jump on the internet to assemble statistics explaining why everybody sitting in the other bleachers has misunderstood transportation.

Fleet managers don't have that luxury. Their question is less interesting and a considerably more useful, “What does this route cost to operate?”

Then multiply that across the fleet, 180 school days, maintenance schedules, drivers, infrastructure, and buses that have to start tomorrow morning whether Brent had a good day or not.

<PQ> And that's where $6.53 diesel matters. Not because it proves propane is the answer. It changes the cost of being wrong about having no alternative.

A district with all of its fuel exposure in diesel experiences a diesel price shock across the fleet. A mixed fleet has different problems, but it also has options.

Run the Numbers While They're Ugly

This fall gives transportation directors unusually useful numbers for stress-testing their fleets.

Take the current diesel price and calculate fuel cost per route. Run the same routes against realistic propane, gasoline, or other available alternatives. Use actual fuel economy rather than pump-price comparisons. Add infrastructure. Add maintenance. Add acquisition cost. Add grants only after confirming they exist.

Then change the assumptions.

What happens if diesel falls back to $4?

What happens at $5?

What happens if $6 lasts another year?

The point isn't to predict oil prices. It's to find the price at which your fleet economics change.

The fleet manager running propane buses today didn't need to predict a disruption in the Strait of Hormuz. The decision was made years earlier, when diesel was cheaper and diversification looked less urgent.

Maybe that decision worked. Maybe another district ran the same numbers and correctly stayed with diesel.

The point isn't that somebody guessed the future. They decided how much exposure to one fuel source they were willing to carry. That's the irritating thing about managing risk. By the time everybody agrees you needed a Plan B, Plan B has gotten expensive too.

Meanwhile, diesel’s average price was $6.43 when I started this article.

Now it's $6.53. Here in the Los Angeles area, it’s $8.43.

I should probably stop writing before Thursday.