Gas vs. Diesel – What’s the Difference?


On the surface, gas and diesel seem to be the same thing to the average person. They both are sold at the fuel station, they both come out of the pump and they both make your engine go.

But you can’t simplify something like that so easily. Gasoline and diesel work differently and the engines that run on them have different attributes.

The first difference between the two is the crude oil that is used to make the product. Gasoline is made of the lightest (density) crude oil. Diesel, meanwhile, comes from slightly heavier crude and is actually a step above jet fuel when it comes to the heaviness of the crude.

Because gasoline is lighter (less dense) it is more flammable and more volatile. That’s why when you turn the key on a gas engine, the spark plug fires and the gasoline detonates immediately to start the engine. Diesel, meanwhile, has to be compressed to a much higher temperature and then it detonates without the need of a spark.

Density is important in another area, and it’s one area where diesel engine owners love to talk about: miles per gallon. Because diesel is denser, it has more “stuff” packed into each gallon, and that stuff is energy. It’s thicker so it has more energy in it and that means the automobile needs to use less of it to run.

You would think that makes diesel a preferred choice for so many people, but it’s not. Why? Because all that compression required means that the engine needs to be built to do all that compressing. And that is more expensive than it is to build an engine that can run on just gasoline.

Need another reason why diesel is not the more popular choice of the two? It has to do with temperature. Diesel needs high temperatures to detonate, and if you live in a place like Alaska, you’re going to have a really hard time getting your engine to turn over when it is ridiculously cold.

Diesel is not quite as popular as gasoline when it comes to where you can find it, but it is hardly difficult. A lot of gas stations will have one or two diesel pumps in addition to many more gasoline pumps. And places that cater to trucking will always have tons of diesel to sell.

When it comes to price, diesel used to have a huge advantage. But the gap has not only narrowed, it has disappeared. Diesel is now more expensive than gasoline, in part because the federal government charges a higher excise tax on diesel than it does on gasoline. Distribution and marketing also cost a lot more with diesel than gasoline so that adds to the price.

Consider that gas mileage with gasoline engines has been improving dramatically in recent years. That helps narrow the gap with diesel, and when the prices of the cars up front are compared, it’s hard to argue with the fact that gasoline can hold its own in the debate.

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