Many gas taxes, but falling over time

Posted by Don Fullerton on Apr 1, 2011

Filed Under (Environmental Policy, U.S. Fiscal Policy)

Per gallon of gasoline, are we paying more in taxes over the years, or less?   In my last post, I examined the Federal gas tax and inflation adjustments.  As it turns out, the overall price of gasoline adjusted for inflation just hasn’t changed that much over the past fifty years!  Regarding the Federal tax of 18.4 cents per gallon as a tool to collect revenue, however, the impact is significantly weakened by inflation.  It is a “unit tax” (fixed over time per unit of gasoline), and so it becomes a smaller fraction of price as the gas price rises.  In contrast, any “ad valorem” tax would be a fixed percentage of price (like an 8% sales tax).  When inflation increases the price, an ad valorem tax rises with it.

State and local gas taxes in Illinois are a bit more complicated. In 1990, the State of Illinois raised the gas tax from 16 cents to the current 19 cents per gallon – another “unit” tax.  The flat blue line in the figure below looks at that same fixed 19 cents per gallon since 1990.  The orange line shows its “real” value, adjusted for inflation, all in current 2011 dollars.  It shows that the 19 cents today is really the equivalent of 33 cents back in 1990.  So the real value of the state’s unit tax on gasoline has fallen from 33 cents to 19 cents per gallon.

In addition to the 19 cent per gallon state gas tax, we also pay 2 cents per gallon to the city of Urbana.  Furthermore, gasoline is subject to the general sales tax, which in Urbana is 8.75%.  (It is composed of 5% to the state, 2.25% to the city, 0.5% to the county, and another 1% to the school district). 

Here is how it all works.  Suppose the net-of-tax price of gas kept by the service station is exactly 3 dollars.  Then the combined state and local ad valorem sales tax (8.75%) applies to that $3.00 per gallon.  That tax would be $0.2625 (in other words, 26.25 cents).  Then the federal unit tax is 18.4 cents, the state unit gas tax is 19 cents, and the city unit gas tax is 2 cents.  The total of all those taxes is 75.65 cents per gallon.  These four major taxes per gallon are shown in the table.

Level of Tax

Tax in Cents per gallon

Federal unit tax


Illinois unit tax

Urbana unit tax


Combined sales tax





That total 76-cent tax adds to the $3 per gallon price, and you pay $3.76 per gallon.   (And actually, a few other minor taxes are ignored here, such as the “Underground Storage Tank” fee and other environmental fees!)

 Yet only the ad valorem sales tax can keep up with inflation.  With every year that a unit tax on gasoline is not updated, the tax loses its value and fails to collect as much real revenue.   The State of Illinois revenue from the 19 cent gas tax is falling in real terms with inflation, as all the necessary expenditures by the State are rising.