Diesel is taxed more than gasoline because the vehicles that burn it — mostly heavy commercial trucks — cause far more damage to roads than passenger cars, and because a gallon of diesel contains more energy and moves a vehicle farther than a gallon of gasoline. The federal excise tax on diesel is 24.4 cents per gallon; on gasoline it is 18.4 cents. That six-cent gap is Congress’s way of making the fuel responsible for the most wear on highways and bridges contribute more toward fixing them.
The Two Rates and What’s In Them
Both taxes are imposed under 26 U.S.C. §4081 and collected when fuel leaves a refinery or terminal, so by the time you pump a gallon at the station, the tax is already baked into the price.1Office of the Law Revision Counsel. 26 USC 4081: Imposition of Tax2U.S. Department of the Treasury. Report to the Congress on Evasion of the Federal Gasoline Excise Tax The base rate is 18.3 cents for gasoline and 24.3 cents for diesel. Every gallon then carries an additional 0.1 cent for the Leaking Underground Storage Tank Trust Fund, which the EPA uses to clean up leaking fuel tanks. That brings the effective totals to 18.4 and 24.4 cents.3U.S. Environmental Protection Agency (EPA). Leaking Underground Storage Tank Trust Fund States add their own fuel taxes on top of the federal rate, and many states also tax diesel more heavily than gasoline, widening the gap further at the pump.
Heavy Trucks Do Most of the Damage
The main reason for the federal split is a user-pays principle written into the Highway Trust Fund. Fuel excise taxes supply roughly 83 percent of the fund’s dedicated revenue, and the fund pays for highway maintenance and construction.4Tax Policy Center. What Is the Highway Trust Fund, and How Is It Financed? Since long-haul freight trucks, dump trucks, and heavy commercial vehicles almost all run on diesel, taxing diesel more heavily shifts a bigger share of the repair bill onto the operators whose vehicles cause the wear.
The size of the disparity between what a truck does to a road and what a car does is bigger than most drivers realize. Engineers use the fourth-power rule, developed from the AASHO Road Test in the early 1960s: doubling the load on an axle multiplies the damage it causes by about sixteen. A fully loaded tractor-trailer at the 80,000-pound federal weight limit has roughly the same impact on an interstate as 9,600 passenger cars.5U.S. Government Accountability Office. Truck Weight and Its Effect on Highways Federal law caps single-axle loads at 20,000 pounds and total vehicle weight at 80,000 pounds on the Interstate System, with the exact allowable weight tied to axle count and spacing under the federal Bridge Formula.6Federal Highway Administration. Bridge Formula Weights Even fully within those limits, a truck’s wear on pavement is orders of magnitude beyond what any car inflicts. The six-cent diesel premium is one lever Congress uses to close that gap.
Diesel Has More Energy Per Gallon
There is a physics argument for the split too. Diesel fuel packs about 13 percent more energy per gallon than gasoline, which is why diesel engines get better mileage.7Alternative Fuels Data Center. Fuel Properties Comparison If both fuels were taxed at the same per-gallon rate, diesel drivers would end up paying less tax per mile of road used, because each gallon carries them farther. The higher diesel rate narrows that per-mile disparity. It isn’t a perfect equalizer — vehicle weight and efficiency vary — but it prevents diesel’s energy advantage from turning into a discount on infrastructure funding.
When Diesel Isn’t Taxed at the Highway Rate
Not every gallon of diesel pays 24.4 cents. Diesel sold for off-road use in farming, construction, and similar work is dyed red and exempt from the federal highway excise tax, because those vehicles never touch public roads.8Office of the Law Revision Counsel. 26 USC 4041: Imposition of Tax Businesses that buy regular undyed diesel for qualifying off-road purposes can claim a refund of the excise tax on IRS Form 4136.9Internal Revenue Service. Instructions for Form 4136 and Schedule A
Enforcement is strict. Putting dyed diesel in a vehicle that drives on public highways, when you knew or should have known the fuel was dyed, carries a penalty of the greater of $1,000 or $10 per gallon, with escalating fines for repeat offenders, plus a back-up tax of 24.4 cents per gallon on the fuel itself.10Internal Revenue Service. Publication 510, Excise Taxes
Heavy Trucks Also Pay a Separate Weight Tax
The diesel premium isn’t the only charge aimed at heavy vehicles. Any highway vehicle with a taxable gross weight of 55,000 pounds or more owes an annual Heavy Vehicle Use Tax, reported on IRS Form 2290, on a sliding scale that tops out at $550 a year for vehicles over 75,000 pounds.11Office of the Law Revision Counsel. 26 USC 4481: Imposition of Tax12Internal Revenue Service. Instructions for Form 2290 (Rev. July 2026) Pickups, vans, and passenger vehicles fall well below that threshold, so this tax lands almost entirely on commercial operators. It reinforces the same principle behind the fuel-tax gap: heavier vehicles pay more because they cost more to accommodate.
When Congress Decided Diesel Should Pay More
The gap is a policy choice, not a permanent feature of the tax code. From 1959 through early 1983, gasoline and diesel were taxed at the same 4 cents per gallon. The Surface Transportation Assistance Act of 1982 raised both fuels equally to 9 cents.13Federal Highway Administration. Appendix K: Historical Federal Fuel Tax Rates
The split arrived with the Deficit Reduction Act of 1984, which raised diesel to 15 cents while leaving gasoline at 9. That was the first time Congress wrote into the tax code that diesel should pay more per gallon than gasoline. The Omnibus Budget Reconciliation Act of 1993 set the base rates at their current 18.3 and 24.3 cents, effective January 1996, and neither has changed since.13Federal Highway Administration. Appendix K: Historical Federal Fuel Tax Rates The reasoning behind the six-cent gap — road damage and energy density — has stayed constant for the better part of forty years, even as the dollar figures themselves have lost more than half their real value to inflation.