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The price of diesel fuel—which moves tractors, trains, and ships around the world—has recently surged, almost doubling in the last two years. The causes of that increase are wide-ranging, from the wars in Iran and Ukraine to policy decisions in Europe and Asia. The resulting crisis is already hitting anyone who uses a diesel-powered vehicle and could soon affect consumers everywhere.

What exactly is diesel? How did Europe become so dependent on it? And who has leverage in the current crisis?

The price of diesel fuel—which moves tractors, trains, and ships around the world—has recently surged, almost doubling in the last two years. The causes of that increase are wide-ranging, from the wars in Iran and Ukraine to policy decisions in Europe and Asia. The resulting crisis is already hitting anyone who uses a diesel-powered vehicle and could soon affect consumers everywhere.

What exactly is diesel? How did Europe become so dependent on it? And who has leverage in the current crisis?

Those are just a few of the questions that came up in my recent conversation with FP economics columnist Adam Tooze on the podcast we co-host, Ones and Tooze. What follows is an excerpt, edited for length and clarity. For the full conversation, look for Ones and Tooze wherever you get your podcasts. And check out Adam’s Substack newsletter.

Cameron Abadi: What is diesel exactly, and what makes it distinct as a fuel?

Adam Tooze: In the process of refining oil, which we’re all getting familiar with as a result of this crisis—it does feel like [U.S. President] Donald Trump’s foreign policy is God’s way of teaching us all chemical engineering—you basically cook the heavy oil, and as you warm it up, different fractions of the oil come off in the refining in these tall towers they have, right? There are very light gases that come off first, because they evaporate off the heavy oil first, and then you get regular benzene and petrol.

Then, lower down, you get heavier products—bigger molecules, basically. At the very bottom, you get something that’s basically tar and is used in road surfacing. But in the middle tier, you get heavy molecules with lots of carbon atoms that are still in various ways easily combustible—not quite as prone to combusting under ignition as petrol, but nevertheless combustible. Diesel is a cocktail of these ingredients in the middle range of the refining stack.

When you encounter diesel, it’s much more oily than regular fuel. Regular fuel is kind of terrifyingly … it feels light if it splashes on your skin, right? Diesel is oily. The thing with diesel is that you want it to spontaneously ignite in hot air, which has to do with the design of the diesel engine. Whereas the classic internal combustion engine injects an emulsion—a cloud of air mixed with petrol and then igniting it with a spark plug—the diesel engine instead compresses air, generating enormous heat in the air.

You don’t really need a spark plug if you have a fuel type like diesel, which when it’s injected into the hot air will spontaneously combust. The result is it produces a much more uniform flame. The problem with a standard internal combustion engine is you basically got a cloud of petrol in air and then you ignite it, so you get an uneven spread of the flame. There’s an awful lot of fancy engineering I used to be totally into as a kid about how you design that combustion chamber and where the air-fuel combination comes in and how you maximize it.

All of that disappears with diesel because you’re just going to compress the air and then inject the fuel into the right place. The beauty of that is several different things, but one crucial one is that you can make the engines really, really big because you can control the way in which the combustion takes place, because it’s going to be uniform across the chamber. With a standard internal combustion engine with a spark plug, you’ve got one flash and then the flame has to spread. Microseconds, of course—but in terms of the efficiency of an engine, as the cylinder gets bigger and bigger, that gets more and more problematic.

So you can’t make super big regular internal combustion engines, whereas you can make diesel engines that are the size of houses, the ones that drive giant ships.

CA: What is the story behind Europe becoming so much more reliant on diesel than the United States? How did Europe become such a diesel continent?

AT: In Europe, there was always a branch of standard passenger vehicles that were diesel, Mercedes-Benz in particular. But only about 10 or 11 percent of European passenger cars were diesel in the late ’80s. By the early........

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