Diesel vs. Gasoline: Engines, Mileage and Prices

Updated November 13, 2026

Diesel and gasoline both come from crude oil, but they are different fuels, burned in different engines, and priced in different markets. Here is what that means for drivers.

How the engines differ

A gasoline engine mixes fuel with air and ignites it with a spark plug. A diesel engine has no spark plugs: it compresses air until it is hot enough that injected diesel fuel ignites on its own. Diesel engines run at higher compression, which makes them efficient and good at producing torque – the reason they dominate trucking, farming, construction and heavy pickups.

The two fuels are not interchangeable. Putting gasoline in a diesel vehicle, or diesel in a gasoline car, can cause serious damage. Diesel pump nozzles and handles are often colored differently to help prevent mistakes.

Energy and mileage

A gallon of diesel contains more energy than a gallon of gasoline, and diesel engines convert that energy efficiently. That is why a diesel version of a vehicle usually travels farther per gallon than its gasoline version. When comparing costs, look at cost per mile, not just price per gallon. Our fuel cost calculator lets you choose diesel and enter your vehicle’s MPG.

What on-highway diesel is

The diesel sold at U.S. stations for road vehicles is ultra-low sulfur diesel (ULSD), which EIA defines as diesel fuel containing a maximum of 15 parts per million of sulfur. EIA’s weekly diesel price is the cash self-serve price of on-highway diesel, collected every Monday from a sample of truck stops and service stations in the continental United States.

Why diesel and gasoline prices move differently

• Different demand. Gasoline demand is driven by passenger travel and peaks in summer. Diesel demand follows freight, farming and industry, and diesel competes with heating oil – a very similar fuel – in winter.
• Global trade. Diesel and other distillates are widely traded internationally, so diesel prices are sensitive to supply problems abroad.
• Taxes. EIA reports that the federal tax on on-highway diesel is 24.4 cents per gallon (a 24.3-cent excise tax plus a 0.1-cent Leaking Underground Storage Tank fee), compared with 18.4 cents for gasoline. State taxes on diesel also differ from those on gasoline.
• Emission controls. Producing ultra-low sulfur fuel and the vehicles’ emission systems add cost.

Compare current prices

See this week’s U.S. averages for gasoline and diesel, or the diesel figure for your area on the state pages. EIA publishes weekly diesel prices for the U.S., each PADD region and subregion, the West Coast excluding California, and California. Background reading: EIA: Diesel fuel explained.