Federal gas tax: 18.4 cents per gallon, unchanged since 1993
The federal gasoline excise is 18.4 cents per gallon (18.3 cents fuel tax plus 0.1 cent LUST trust fund). The federal diesel excise is 24.4 cents per gallon. Both rates have been unchanged since 1 October 1993. Revenue flows to the Highway Trust Fund. [FHWA · 13 Jul 2026]
The rate and the math
On a $3.87 national average pump price, the 18.4-cent federal excise is 6.2 percent. On a $4.59 California gallon it is 4.0 percent.
Why it has not been indexed
Indexing was politically impossible through three decades of Republican and Democratic majorities. Real (inflation-adjusted) federal revenue per mile driven has fallen by roughly half since 1993, which is why the Highway Trust Fund regularly faces shortfalls and Congress must transfer general-fund money in.
Where the revenue goes
Highway Trust Fund (Highway Account and Mass Transit Account). About 84 percent to highways, 16 percent to transit.