How Federal and State Taxes Make Diesel Cost More

When diesel costs more than gasoline, taxes explain part of the difference—but usually not all of it. The federal government charges 6 cents more per gallon on highway diesel than on gasoline. State taxes can widen that gap, narrow it, or partly offset it.

To understand what you pay, it helps to separate three things: fuel taxes, the cost of making cleaner diesel, and the broader market forces that move pump prices. They all affect your bill, but they work differently.

How the Taxes Add Up

For on-road diesel—the fuel you buy for highway vehicles—federal and state fuel taxes are included in the pump price. You generally do not see them added at checkout as a separate charge.

Using the Energy Information Administration’s January 2026 state averages, the comparison looks like this:

The federal figures include a 0.1-cent-per-gallon underground-storage-tank fee on both fuels. Because that fee is the same for gasoline and diesel, it does not contribute to the difference between them. These figures come from the EIA’s fuel-tax summary.

The important distinction is between the total tax burden and the extra tax on diesel:

• Diesel’s combined federal and average state charges are 59.90 cents per gallon.
• Gasoline also carries substantial taxes: 51.67 cents per gallon.
• The difference is therefore 8.23 cents, not nearly 60 cents.

To explain why diesel costs more than gasoline, compare the taxes on the two fuels—not diesel’s taxes with zero.

On a 20-gallon purchase, that national-average tax difference amounts to about $1.65.

Why your state matters

The federal rates are the same nationwide, but states set their own fuel-tax rates. A state does not have to tax diesel more heavily than gasoline.

That means the national average is a useful benchmark, not a precise estimate for every driver. Your actual tax burden depends on where you buy fuel, and county or other local charges may add more.

For a local comparison, you need to look at both fuels in the same jurisdiction. Comparing diesel in one state with gasoline in another mixes together differences in taxes and differences in fuel markets.

Why Is the Federal Diesel Tax Higher?

The federal 6-cent diesel–gasoline differential was adopted in 1984 to make heavier trucks—which predominantly use diesel—pay a greater share of highway costs. The Federal Highway Administration’s highway-cost-allocation work describes that policy background.

The basic idea is cost allocation: deciding how much different road users should contribute toward the roads they use.

But taxing diesel more is a broad way to pursue that goal. It is not a precise calculation of the road costs caused by each vehicle.

A proxy for heavy trucks, not a vehicle-weight bill

A proxy is an easily measured substitute for something harder to measure directly. In this case, diesel purchases serve as a rough stand-in for use by heavy trucks.

The fuel tax does not check:

• How much your vehicle weighs.
• How heavily it is loaded.
• Which roads it travels.
• How much road wear that particular trip causes.

As a result, a diesel passenger car pays the higher federal rate too, even though it is not a heavy commercial truck.

You can think of the tax as a broad contribution collected through fuel purchases, rather than an itemized bill for each vehicle’s effect on the highway.

How Much of the Pump-Price Gap Can Taxes Explain?

In the January 2026 national-average comparison, taxes and fees account for about 8 cents per gallon of diesel’s price disadvantage.

That is meaningful, but it is not enough to explain a large spread.

Suppose you see diesel priced 50 cents per gallon above gasoline. If the tax difference at that location were 8.23 cents, taxes would account for only that portion. The remaining 41.77 cents would have to come from other costs and market conditions.

This is also why a persistent tax difference is a poor explanation for a rapidly changing price gap:

• A fixed cents-per-gallon tax difference creates a relatively steady contribution to the gap.
• A large or quickly changing spread requires you to look beyond that fixed difference.

State tax changes can affect prices, of course. But the longstanding federal 6-cent differential cannot, by itself, explain why the diesel–gasoline spread suddenly expands or contracts.

Cleaner Diesel Costs More to Make—But That Is Not a Tax

Another often-mentioned reason for diesel’s cost is ultra-low-sulfur diesel, usually shortened to ULSD.

ULSD contains no more than 15 parts per million of sulfur. “Parts per million” describes a very small concentration: here, no more than 15 parts sulfur for every million parts of fuel by mass. The previous U.S. highway-diesel limit was 500 parts per million.

Reducing sulfur allows modern diesel exhaust-control systems to work effectively. ULSD was phased in for highway use from 2006 to 2010 and is now the required highway diesel fuel, according to the Environmental Protection Agency.

How refineries remove the sulfur

Refineries do not simply strain sulfur out through a filter. They use hydrotreating—a chemical process that removes sulfur from the molecules containing it.

The process has three main steps:

1. Heat and pressurize the fuel. A diesel-range refinery stream is mixed with hydrogen and sent through a pressurized reactor.
2. Use a catalyst to help the reaction. A catalyst is a material that helps a chemical reaction proceed. Common systems use cobalt–molybdenum or nickel–molybdenum supported on alumina. Hydrogen reacts with sulfur-containing molecules, producing hydrogen sulfide, a sulfur-bearing gas.
3. Separate and recover the sulfur. The refinery removes the hydrogen sulfide from the treated fuel and gas streams. It can then recover the sulfur as elemental sulfur, commonly in equipment called a Claus sulfur-recovery unit.

This requires hydrogen, heat, compressors, high-pressure equipment, catalysts, and sulfur-handling systems—all of which cost money.

The last traces of sulfur are especially challenging. Easy-to-remove compounds react first; those left near the 15-parts-per-million limit are harder to treat. Depending on the incoming fuel stream, a refinery may need higher pressure, more hydrogen, a more capable catalyst, or more time in the reactor.

Removing the last tiny amount of sulfur can cost disproportionately more than removing the first large amount.

Is there a fixed ULSD surcharge?

No. When ULSD was introduced, the EPA estimated an additional production-and-distribution cost of about 4–5 cents per gallon compared with the older fuel. That was a historical estimate—not a separate tax or a permanent surcharge you can identify on today’s receipt. See the EPA’s ULSD cost discussion.

You should therefore not simply add “8 cents in extra taxes” and “5 cents for ULSD” and assume you have explained today’s price gap. The tax comparison is tied to particular rates and a date; the ULSD estimate compared a new fuel standard with the older one.

The Bottom Line

When you compare diesel with gasoline, keep these categories separate:

Taxes give diesel a modest built-in price disadvantage. In the January 2026 national-average comparison, that disadvantage was about 8 cents per gallon. If the spread you see is much larger—or changing quickly—the tax system is only part of the explanation.